diff --git a/apps/yaak-client/lib/theme/appearance.ts b/apps/yaak-client/lib/theme/appearance.ts
index 4d199e90..00448544 100644
--- a/apps/yaak-client/lib/theme/appearance.ts
+++ b/apps/yaak-client/lib/theme/appearance.ts
@@ -1,48 +1,8 @@
-import { getCurrentWebviewWindow } from '@tauri-apps/api/webviewWindow';
-
-export type Appearance = 'light' | 'dark';
-
-export function getCSSAppearance(): Appearance {
-  return window.matchMedia('(prefers-color-scheme: dark)').matches ? 'dark' : 'light';
-}
-
-export async function getWindowAppearance(): Promise<Appearance> {
-  const a = await getCurrentWebviewWindow().theme();
-  return a ?? getCSSAppearance();
-}
-
-/**
- * Subscribe to appearance (dark/light) changes. Note, we use Tauri Window appearance instead of
- * CSS appearance because CSS won't fire the way we handle window theme management.
- */
-export function subscribeToWindowAppearanceChange(
-  cb: (appearance: Appearance) => void,
-): () => void {
-  const container = {
-    unsubscribe: () => {},
-  };
-
-  getCurrentWebviewWindow()
-    .onThemeChanged((t) => {
-      cb(t.payload);
-    })
-    .then((l) => {
-      container.unsubscribe = l;
-    });
-
-  return () => container.unsubscribe();
-}
-
-export function resolveAppearance(
-  preferredAppearance: Appearance,
-  appearanceSetting: string,
-): Appearance {
-  const appearance = appearanceSetting === 'system' ? preferredAppearance : appearanceSetting;
-  return appearance === 'dark' ? 'dark' : 'light';
-}
-
-export function subscribeToPreferredAppearance(cb: (a: Appearance) => void) {
-  cb(getCSSAppearance());
-  getWindowAppearance().then(cb);
-  subscribeToWindowAppearanceChange(cb);
-}
+export type { Appearance } from "@yaakapp-internal/theme";
+export {
+  getCSSAppearance,
+  getWindowAppearance,
+  resolveAppearance,
+  subscribeToPreferredAppearance,
+  subscribeToWindowAppearanceChange,
+} from "@yaakapp-internal/theme";
diff --git a/apps/yaak-client/lib/theme/themes.ts b/apps/yaak-client/lib/theme/themes.ts
index ce84f842..c1c44e28 100644
--- a/apps/yaak-client/lib/theme/themes.ts
+++ b/apps/yaak-client/lib/theme/themes.ts
@@ -1,14 +1,21 @@
-import type { GetThemesResponse } from '@yaakapp-internal/plugins';
-import { invokeCmd } from '../tauri';
-import type { Appearance } from './appearance';
-import { resolveAppearance } from './appearance';
+import type { GetThemesResponse } from "@yaakapp-internal/plugins";
+import { defaultDarkTheme, defaultLightTheme } from "@yaakapp-internal/theme";
+import { invokeCmd } from "../tauri";
+import type { Appearance } from "./appearance";
+import { resolveAppearance } from "./appearance";
+
+export { defaultDarkTheme, defaultLightTheme } from "@yaakapp-internal/theme";
 
 export async function getThemes() {
-  const themes = (await invokeCmd<GetThemesResponse[]>('cmd_get_themes')).flatMap((t) => t.themes);
+  const themes = (
+    await invokeCmd<GetThemesResponse[]>("cmd_get_themes")
+  ).flatMap((t) => t.themes);
   themes.sort((a, b) => a.label.localeCompare(b.label));
   // Remove duplicates, in case multiple plugins provide the same theme
-  const uniqueThemes = Array.from(new Map(themes.map((t) => [t.id, t])).values());
-  return { themes: [yaakDark, yaakLight, ...uniqueThemes] };
+  const uniqueThemes = Array.from(
+    new Map(themes.map((t) => [t.id, t])).values(),
+  );
+  return { themes: [defaultDarkTheme, defaultLightTheme, ...uniqueThemes] };
 }
 
 export async function getResolvedTheme(
@@ -23,88 +30,16 @@ export async function getResolvedTheme(
   const darkThemes = themes.filter((t) => t.dark);
   const lightThemes = themes.filter((t) => !t.dark);
 
-  const dark = darkThemes.find((t) => t.id === themeDark) ?? darkThemes[0] ?? yaakDark;
-  const light = lightThemes.find((t) => t.id === themeLight) ?? lightThemes[0] ?? yaakLight;
+  const dark =
+    darkThemes.find((t) => t.id === themeDark) ??
+    darkThemes[0] ??
+    defaultDarkTheme;
+  const light =
+    lightThemes.find((t) => t.id === themeLight) ??
+    lightThemes[0] ??
+    defaultLightTheme;
 
-  const active = appearance === 'dark' ? dark : light;
+  const active = appearance === "dark" ? dark : light;
 
   return { dark, light, active };
 }
-
-const yaakDark = {
-  id: 'yaak-dark',
-  label: 'Yaak',
-  dark: true,
-  base: {
-    surface: 'hsl(244,23%,14%)',
-    surfaceHighlight: 'hsl(244,23%,20%)',
-    text: 'hsl(245,23%,85%)',
-    textSubtle: 'hsl(245,18%,58%)',
-    textSubtlest: 'hsl(245,18%,45%)',
-    border: 'hsl(244,23%,25%)',
-    primary: 'hsl(266,100%,79%)',
-    secondary: 'hsl(245,23%,60%)',
-    info: 'hsl(206,100%,63%)',
-    success: 'hsl(150,99%,44%)',
-    notice: 'hsl(48,80%,63%)',
-    warning: 'hsl(28,100%,61%)',
-    danger: 'hsl(342,90%,68%)',
-  },
-  components: {
-    button: {
-      primary: 'hsl(266,100%,71.1%)',
-      secondary: 'hsl(244,23%,54%)',
-      info: 'hsl(206,100%,56.7%)',
-      success: 'hsl(150,99%,37.4%)',
-      notice: 'hsl(48,80%,50.4%)',
-      warning: 'hsl(28,100%,54.9%)',
-      danger: 'hsl(342,90%,61.2%)',
-    },
-    dialog: {
-      border: 'hsl(244,23%,24%)',
-    },
-    sidebar: {
-      surface: 'hsl(243,23%,16%)',
-      border: 'hsl(244,23%,22%)',
-    },
-    responsePane: {
-      surface: 'hsl(243,23%,16%)',
-      border: 'hsl(246,23%,23%)',
-    },
-    appHeader: {
-      surface: 'hsl(244,23%,12%)',
-      border: 'hsl(244,23%,21%)',
-    },
-  },
-};
-
-const yaakLight = {
-  id: 'yaak-light',
-  label: 'Yaak',
-  dark: false,
-  base: {
-    surface: 'hsl(0,0%,100%)',
-    surfaceHighlight: 'hsl(218,24%,87%)',
-    text: 'hsl(217,24%,10%)',
-    textSubtle: 'hsl(217,24%,40%)',
-    textSubtlest: 'hsl(217,24%,58%)',
-    border: 'hsl(217,22%,90%)',
-    primary: 'hsl(266,100%,60%)',
-    secondary: 'hsl(220,24%,50%)',
-    info: 'hsl(206,100%,40%)',
-    success: 'hsl(139,66%,34%)',
-    notice: 'hsl(45,100%,34%)',
-    warning: 'hsl(30,100%,36%)',
-    danger: 'hsl(335,75%,48%)',
-  },
-  components: {
-    sidebar: {
-      surface: 'hsl(220,20%,98%)',
-      border: 'hsl(217,22%,88%)',
-      surfaceHighlight: 'hsl(217,25%,90%)',
-    },
-  },
-};
-
-export const defaultDarkTheme = yaakDark;
-export const defaultLightTheme = yaakLight;
diff --git a/apps/yaak-client/lib/theme/window.ts b/apps/yaak-client/lib/theme/window.ts
index a5dd5939..a369d94f 100644
--- a/apps/yaak-client/lib/theme/window.ts
+++ b/apps/yaak-client/lib/theme/window.ts
@@ -1,386 +1,13 @@
-import type { Theme, ThemeComponentColors } from '@yaakapp-internal/plugins';
-import { defaultDarkTheme, defaultLightTheme } from './themes';
-import { YaakColor } from './yaakColor';
-
-export type YaakColors = {
-  surface: YaakColor;
-  surfaceHighlight?: YaakColor;
-  surfaceActive?: YaakColor;
-
-  text: YaakColor;
-  textSubtle?: YaakColor;
-  textSubtlest?: YaakColor;
-
-  border?: YaakColor;
-  borderSubtle?: YaakColor;
-  borderFocus?: YaakColor;
-
-  shadow?: YaakColor;
-  backdrop?: YaakColor;
-  selection?: YaakColor;
-
-  primary?: YaakColor;
-  secondary?: YaakColor;
-  info?: YaakColor;
-  success?: YaakColor;
-  notice?: YaakColor;
-  warning?: YaakColor;
-  danger?: YaakColor;
-};
-
-export type YaakTheme = {
-  id: string;
-  name: string;
-  base: YaakColors;
-  components?: Partial<{
-    dialog: Partial<YaakColors>;
-    menu: Partial<YaakColors>;
-    toast: Partial<YaakColors>;
-    sidebar: Partial<YaakColors>;
-    responsePane: Partial<YaakColors>;
-    appHeader: Partial<YaakColors>;
-    button: Partial<YaakColors>;
-    banner: Partial<YaakColors>;
-    templateTag: Partial<YaakColors>;
-    urlBar: Partial<YaakColors>;
-    editor: Partial<YaakColors>;
-    input: Partial<YaakColors>;
-  }>;
-};
-
-export type YaakColorKey = keyof ThemeComponentColors;
-
-type ComponentName = keyof NonNullable<YaakTheme['components']>;
-
-type CSSVariables = Record<YaakColorKey, string | undefined>;
-
-function themeVariables(
-  theme: Theme,
-  component?: ComponentName,
-  base?: CSSVariables,
-): CSSVariables | null {
-  const cmp =
-    component == null
-      ? theme.base
-      : (theme.components?.[component] ?? ({} as ThemeComponentColors));
-  const c = (s: string | undefined) => yc(theme, s);
-  const vars: CSSVariables = {
-    surface: cmp.surface,
-    surfaceHighlight: cmp.surfaceHighlight ?? c(cmp.surface)?.lift(0.06).css(),
-    surfaceActive: cmp.surfaceActive ?? c(cmp.primary)?.lower(0.2).translucify(0.8).css(),
-    backdrop: cmp.backdrop ?? c(cmp.surface)?.lower(0.2).translucify(0.2).css(),
-    selection: cmp.selection ?? c(cmp.primary)?.lower(0.1).translucify(0.7).css(),
-    border: cmp.border ?? c(cmp.surface)?.lift(0.11)?.css(),
-    borderSubtle: cmp.borderSubtle ?? c(cmp.border)?.lower(0.06)?.css(),
-    borderFocus: c(cmp.info)?.translucify(0.5)?.css(),
-    text: cmp.text,
-    textSubtle: cmp.textSubtle ?? c(cmp.text)?.lower(0.2)?.css(),
-    textSubtlest: cmp.textSubtlest ?? c(cmp.text)?.lower(0.3)?.css(),
-    shadow:
-      cmp.shadow ??
-      YaakColor.black()
-        .translucify(theme.dark ? 0.7 : 0.93)
-        .css(),
-    primary: cmp.primary,
-    secondary: cmp.secondary,
-    info: cmp.info,
-    success: cmp.success,
-    notice: cmp.notice,
-    warning: cmp.warning,
-    danger: cmp.danger,
-  };
-
-  // Extend with base
-  for (const [k, v] of Object.entries(vars)) {
-    if (!v && base?.[k as YaakColorKey]) {
-      vars[k as YaakColorKey] = base[k as YaakColorKey];
-    }
-  }
-
-  return vars;
-}
-
-function templateTagColorVariables(color: YaakColor | null): Partial<CSSVariables> {
-  if (color == null) return {};
-
-  return {
-    text: color.lift(0.7).css(),
-    textSubtle: color.lift(0.4).css(),
-    textSubtlest: color.css(),
-    surface: color.lower(0.2).translucify(0.8).css(),
-    border: color.translucify(0.6).css(),
-    borderSubtle: color.translucify(0.8).css(),
-    surfaceHighlight: color.lower(0.1).translucify(0.7).css(),
-  };
-}
-
-function toastColorVariables(color: YaakColor | null): Partial<CSSVariables> {
-  if (color == null) return {};
-
-  return {
-    text: color.lift(0.8).css(),
-    textSubtle: color.lift(0.8).translucify(0.3).css(),
-    surface: color.translucify(0.9).css(),
-    surfaceHighlight: color.translucify(0.8).css(),
-    border: color.lift(0.3).translucify(0.6).css(),
-  };
-}
-
-function bannerColorVariables(color: YaakColor | null): Partial<CSSVariables> {
-  if (color == null) return {};
-
-  return {
-    text: color.lift(0.8).css(),
-    textSubtle: color.translucify(0.3).css(),
-    textSubtlest: color.translucify(0.6).css(),
-    surface: color.translucify(0.95).css(),
-    border: color.lift(0.3).translucify(0.8).css(),
-  };
-}
-
-function inputCSS(color: YaakColor | null): Partial<CSSVariables> {
-  if (color == null) return {};
-
-  const theme: Partial<ThemeComponentColors> = {
-    border: color.css(),
-  };
-
-  return theme;
-}
-
-function buttonSolidColorVariables(
-  color: YaakColor | null,
-  isDefault = false,
-): Partial<CSSVariables> {
-  if (color == null) return {};
-
-  const theme: Partial<ThemeComponentColors> = {
-    text: 'white',
-    surface: color.lower(0.3).css(),
-    surfaceHighlight: color.lower(0.1).css(),
-    border: color.css(),
-  };
-
-  if (isDefault) {
-    theme.text = undefined; // Inherit from parent
-    theme.surface = undefined; // Inherit from parent
-    theme.surfaceHighlight = color.lift(0.08).css();
-  }
-
-  return theme;
-}
-
-function buttonBorderColorVariables(
-  color: YaakColor | null,
-  isDefault = false,
-): Partial<CSSVariables> {
-  if (color == null) return {};
-
-  const vars: Partial<CSSVariables> = {
-    text: color.lift(0.8).css(),
-    textSubtle: color.lift(0.55).css(),
-    textSubtlest: color.lift(0.4).translucify(0.6).css(),
-    surfaceHighlight: color.translucify(0.8).css(),
-    borderSubtle: color.translucify(0.5).css(),
-    border: color.translucify(0.3).css(),
-  };
-
-  if (isDefault) {
-    vars.borderSubtle = color.lift(0.28).css();
-    vars.border = color.lift(0.5).css();
-  }
-
-  return vars;
-}
-
-function variablesToCSS(
-  selector: string | null,
-  vars: Partial<CSSVariables> | null,
-): string | null {
-  if (vars == null) {
-    return null;
-  }
-
-  const css = Object.entries(vars ?? {})
-    .filter(([, value]) => value)
-    .map(([name, value]) => `--${name}: ${value};`)
-    .join('\n');
-
-  return selector == null ? css : `${selector} {\n${indent(css)}\n}`;
-}
-
-function componentCSS(theme: Theme, component: ComponentName): string | null {
-  if (theme.components == null) {
-    return null;
-  }
-
-  const themeVars = themeVariables(theme, component);
-  return variablesToCSS(`.x-theme-${component}`, themeVars);
-}
-
-function buttonCSS(
-  theme: Theme,
-  color: YaakColorKey,
-  colors?: ThemeComponentColors,
-): string | null {
-  const yaakColor = yc(theme, colors?.[color]);
-  if (yaakColor == null) {
-    return null;
-  }
-
-  return [
-    variablesToCSS(`.x-theme-button--solid--${color}`, buttonSolidColorVariables(yaakColor)),
-    variablesToCSS(`.x-theme-button--border--${color}`, buttonBorderColorVariables(yaakColor)),
-  ].join('\n\n');
-}
-
-function bannerCSS(
-  theme: Theme,
-  color: YaakColorKey,
-  colors?: ThemeComponentColors,
-): string | null {
-  const yaakColor = yc(theme, colors?.[color]);
-  if (yaakColor == null) {
-    return null;
-  }
-
-  return [variablesToCSS(`.x-theme-banner--${color}`, bannerColorVariables(yaakColor))].join(
-    '\n\n',
-  );
-}
-
-function toastCSS(theme: Theme, color: YaakColorKey, colors?: ThemeComponentColors): string | null {
-  const yaakColor = yc(theme, colors?.[color]);
-  if (yaakColor == null) {
-    return null;
-  }
-
-  return [variablesToCSS(`.x-theme-toast--${color}`, toastColorVariables(yaakColor))].join('\n\n');
-}
-
-function templateTagCSS(
-  theme: Theme,
-  color: YaakColorKey,
-  colors?: ThemeComponentColors,
-): string | null {
-  const yaakColor = yc(theme, colors?.[color]);
-  if (yaakColor == null) {
-    return null;
-  }
-
-  return [
-    variablesToCSS(`.x-theme-templateTag--${color}`, templateTagColorVariables(yaakColor)),
-  ].join('\n\n');
-}
-
-export function getThemeCSS(theme: Theme): string {
-  theme.components = theme.components ?? {};
-  // Toast defaults to menu styles
-  theme.components.toast = theme.components.toast ?? theme.components.menu ?? {};
-  const { components, id, label } = theme;
-  const colors = Object.keys(theme.base).reduce((prev, key) => {
-    // biome-ignore lint/performance/noAccumulatingSpread: none
-    return { ...prev, [key]: theme.base[key as YaakColorKey] };
-  }, {}) as ThemeComponentColors;
-
-  let themeCSS = '';
-  try {
-    const baseCss = variablesToCSS(null, themeVariables(theme));
-    themeCSS = [
-      baseCss,
-      ...Object.keys(components ?? {}).map((key) => componentCSS(theme, key as ComponentName)),
-      variablesToCSS(
-        '.x-theme-button--solid--default',
-        buttonSolidColorVariables(yc(theme, theme.base.surface), true),
-      ),
-      variablesToCSS(
-        '.x-theme-button--border--default',
-        buttonBorderColorVariables(yc(theme, theme.base.surface), true),
-      ),
-      ...Object.keys(colors ?? {}).map((key) =>
-        buttonCSS(theme, key as YaakColorKey, theme.components?.button ?? colors),
-      ),
-      ...Object.keys(colors ?? {}).map((key) =>
-        bannerCSS(theme, key as YaakColorKey, theme.components?.banner ?? colors),
-      ),
-      ...Object.keys(colors ?? {}).map((key) =>
-        toastCSS(theme, key as YaakColorKey, theme.components?.banner ?? colors),
-      ),
-      ...Object.keys(colors ?? {}).map((key) =>
-        templateTagCSS(theme, key as YaakColorKey, theme.components?.templateTag ?? colors),
-      ),
-    ].join('\n\n');
-  } catch (err) {
-    console.error('Failed to generate CSS', err);
-  }
-
-  return [`/* ${label} */`, `[data-theme="${id}"] {`, indent(themeCSS), '}'].join('\n');
-}
-
-export function addThemeStylesToDocument(rawTheme: Theme | null) {
-  if (rawTheme == null) {
-    console.error('Failed to add theme styles: theme is null');
-    return;
-  }
-
-  const theme = completeTheme(rawTheme);
-  let styleEl = document.head.querySelector('style[data-theme]');
-  if (!styleEl) {
-    styleEl = document.createElement('style');
-    document.head.appendChild(styleEl);
-  }
-
-  styleEl.setAttribute('data-theme', theme.id);
-  styleEl.setAttribute('data-updated-at', new Date().toISOString());
-  styleEl.textContent = getThemeCSS(theme);
-}
-
-export function setThemeOnDocument(theme: Theme | null) {
-  if (theme == null) {
-    console.error('Failed to set theme: theme is null');
-    return;
-  }
-
-  document.documentElement.setAttribute('data-theme', theme.id);
-}
-
-export function indent(text: string, space = '    '): string {
-  return text
-    .split('\n')
-    .map((line) => space + line)
-    .join('\n');
-}
-
-function yc<T extends string | null | undefined>(
-  theme: Theme,
-  s: T,
-): T extends string ? YaakColor : null {
-  if (s == null) return null as never;
-  return new YaakColor(s, theme.dark ? 'dark' : 'light') as never;
-}
-
-export function completeTheme(theme: Theme): Theme {
-  const fallback = theme.dark ? defaultDarkTheme.base : defaultLightTheme.base;
-  const c = (s: string | null | undefined) => yc(theme, s);
-
-  theme.base.primary ??= fallback.primary;
-  theme.base.secondary ??= fallback.secondary;
-  theme.base.info ??= fallback.info;
-  theme.base.success ??= fallback.success;
-  theme.base.notice ??= fallback.notice;
-  theme.base.warning ??= fallback.warning;
-  theme.base.danger ??= fallback.danger;
-
-  theme.base.surface ??= fallback.surface;
-  theme.base.surfaceHighlight ??= c(theme.base.surface)?.lift(0.06)?.css();
-  theme.base.surfaceActive ??= c(theme.base.primary)?.lower(0.2).translucify(0.8).css();
-
-  theme.base.border ??= c(theme.base.surface)?.lift(0.12)?.css();
-  theme.base.borderSubtle ??= c(theme.base.border)?.lower(0.08)?.css();
-
-  theme.base.text ??= fallback.text;
-  theme.base.textSubtle ??= c(theme.base.text)?.lower(0.3)?.css();
-  theme.base.textSubtlest ??= c(theme.base.text)?.lower(0.5)?.css();
-
-  return theme;
-}
+export type {
+  YaakColorKey,
+  YaakColors,
+  YaakTheme,
+} from "@yaakapp-internal/theme";
+export {
+  addThemeStylesToDocument,
+  applyThemeToDocument,
+  completeTheme,
+  getThemeCSS,
+  indent,
+  setThemeOnDocument,
+} from "@yaakapp-internal/theme";
diff --git a/apps/yaak-client/lib/theme/yaakColor.ts b/apps/yaak-client/lib/theme/yaakColor.ts
index 26510c48..513e50b2 100644
--- a/apps/yaak-client/lib/theme/yaakColor.ts
+++ b/apps/yaak-client/lib/theme/yaakColor.ts
@@ -1,158 +1 @@
-import parseColor from 'parse-color';
-
-export class YaakColor {
-  private readonly appearance: 'dark' | 'light' = 'light';
-
-  private hue = 0;
-  private saturation = 0;
-  private lightness = 0;
-  private alpha = 1;
-
-  constructor(cssColor: string, appearance: 'dark' | 'light' = 'light') {
-    try {
-      this.set(cssColor);
-      this.appearance = appearance;
-    } catch (err) {
-      console.log('Failed to parse CSS color', cssColor, err);
-    }
-  }
-
-  static transparent(): YaakColor {
-    return new YaakColor('rgb(0,0,0)', 'light').translucify(1);
-  }
-
-  static white(): YaakColor {
-    return new YaakColor('rgb(0,0,0)', 'light').lower(1);
-  }
-
-  static black(): YaakColor {
-    return new YaakColor('rgb(0,0,0)', 'light').lift(1);
-  }
-
-  set(cssColor: string): YaakColor {
-    let fixedCssColor = cssColor;
-    if (cssColor.startsWith('#') && cssColor.length === 9) {
-      const [r, g, b, a] = hexToRgba(cssColor);
-      fixedCssColor = `rgba(${r},${g},${b},${a})`;
-    }
-    const { hsla } = parseColor(fixedCssColor);
-    this.hue = hsla[0];
-    this.saturation = hsla[1];
-    this.lightness = hsla[2];
-    this.alpha = hsla[3] ?? 1;
-    return this;
-  }
-
-  clone(): YaakColor {
-    return new YaakColor(this.css(), this.appearance);
-  }
-
-  lower(mod: number): YaakColor {
-    return this.appearance === 'dark' ? this._darken(mod) : this._lighten(mod);
-  }
-
-  lift(mod: number): YaakColor {
-    return this.appearance === 'dark' ? this._lighten(mod) : this._darken(mod);
-  }
-
-  minLightness(n: number): YaakColor {
-    const c = this.clone();
-    if (c.lightness < n) {
-      c.lightness = n;
-    }
-    return c;
-  }
-
-  isDark(): boolean {
-    return this.lightness < 50;
-  }
-
-  translucify(mod: number): YaakColor {
-    const c = this.clone();
-    c.alpha = c.alpha - c.alpha * mod;
-    return c;
-  }
-
-  opacify(mod: number): YaakColor {
-    const c = this.clone();
-    c.alpha = this.alpha + (100 - this.alpha) * mod;
-    return c;
-  }
-
-  desaturate(mod: number): YaakColor {
-    const c = this.clone();
-    c.saturation = c.saturation - c.saturation * mod;
-    return c;
-  }
-
-  saturate(mod: number): YaakColor {
-    const c = this.clone();
-    c.saturation = this.saturation + (100 - this.saturation) * mod;
-    return c;
-  }
-
-  lighterThan(c: YaakColor): boolean {
-    return this.lightness > c.lightness;
-  }
-
-  css(): string {
-    const h = this.hue;
-    const s = this.saturation;
-    const l = this.lightness;
-    const a = this.alpha;
-
-    const [r, g, b] = parseColor(`hsl(${h},${s}%,${l}%)`).rgb;
-    return rgbaToHex(r, g, b, a);
-  }
-
-  hexNoAlpha(): string {
-    const h = this.hue;
-    const s = this.saturation;
-    const l = this.lightness;
-
-    const [r, g, b] = parseColor(`hsl(${h},${s}%,${l}%)`).rgb;
-    return rgbaToHexNoAlpha(r, g, b);
-  }
-
-  private _lighten(mod: number): YaakColor {
-    const c = this.clone();
-    c.lightness = this.lightness + (100 - this.lightness) * mod;
-    return c;
-  }
-
-  private _darken(mod: number): YaakColor {
-    const c = this.clone();
-    c.lightness = this.lightness - this.lightness * mod;
-    return c;
-  }
-}
-
-function rgbaToHex(r: number, g: number, b: number, a: number): string {
-  const toHex = (n: number): string => {
-    const hex = Number(Math.round(n)).toString(16);
-    return hex.length === 1 ? `0${hex}` : hex;
-  };
-  return `#${[toHex(r), toHex(g), toHex(b), toHex(a * 255)].join('').toUpperCase()}`;
-}
-
-function rgbaToHexNoAlpha(r: number, g: number, b: number): string {
-  const toHex = (n: number): string => {
-    const hex = Number(Math.round(n)).toString(16);
-    return hex.length === 1 ? `0${hex}` : hex;
-  };
-  return `#${[toHex(r), toHex(g), toHex(b)].join('').toUpperCase()}`;
-}
-
-function hexToRgba(hex: string): [number, number, number, number] {
-  const fromHex = (h: string): number => {
-    if (h === '') return 255;
-    return Number(`0x${h}`);
-  };
-
-  const r = fromHex(hex.slice(1, 3));
-  const g = fromHex(hex.slice(3, 5));
-  const b = fromHex(hex.slice(5, 7));
-  const a = fromHex(hex.slice(7, 9));
-
-  return [r, g, b, a / 255];
-}
+export { YaakColor } from "@yaakapp-internal/theme";
diff --git a/apps/yaak-client/main.tsx b/apps/yaak-client/main.tsx
index 389683cf..626ac317 100644
--- a/apps/yaak-client/main.tsx
+++ b/apps/yaak-client/main.tsx
@@ -1,29 +1,33 @@
-import './main.css';
-import { RouterProvider } from '@tanstack/react-router';
-import { type } from '@tauri-apps/plugin-os';
-import { changeModelStoreWorkspace, initModelStore } from '@yaakapp-internal/models';
-import { StrictMode } from 'react';
-import { createRoot } from 'react-dom/client';
-import { initSync } from './init/sync';
-import { initGlobalListeners } from './lib/initGlobalListeners';
-import { jotaiStore } from './lib/jotai';
-import { router } from './lib/router';
+import "./main.css";
+import { RouterProvider } from "@tanstack/react-router";
+import { type } from "@tauri-apps/plugin-os";
+import {
+  changeModelStoreWorkspace,
+  initModelStore,
+} from "@yaakapp-internal/models";
+import { setPlatformOnDocument } from "@yaakapp-internal/theme";
+import { StrictMode } from "react";
+import { createRoot } from "react-dom/client";
+import { initSync } from "./init/sync";
+import { initGlobalListeners } from "./lib/initGlobalListeners";
+import { jotaiStore } from "./lib/jotai";
+import { router } from "./lib/router";
 
 const osType = type();
-document.documentElement.setAttribute('data-platform', osType);
+setPlatformOnDocument(osType);
 
-window.addEventListener('keydown', (e) => {
+window.addEventListener("keydown", (e) => {
   const rx = /input|select|textarea/i;
 
   const target = e.target;
-  if (e.key !== 'Backspace') return;
+  if (e.key !== "Backspace") return;
   if (!(target instanceof Element)) return;
-  if (target.getAttribute('contenteditable') !== null) return;
+  if (target.getAttribute("contenteditable") !== null) return;
 
   if (
     !rx.test(target.tagName) ||
-    ('disabled' in target && target.disabled) ||
-    ('readOnly' in target && target.readOnly)
+    ("disabled" in target && target.disabled) ||
+    ("readOnly" in target && target.readOnly)
   ) {
     e.preventDefault();
   }
@@ -35,8 +39,8 @@ initModelStore(jotaiStore);
 initGlobalListeners();
 await changeModelStoreWorkspace(null); // Load global models
 
-console.log('Creating React root');
-createRoot(document.getElementById('root') as HTMLElement).render(
+console.log("Creating React root");
+createRoot(document.getElementById("root") as HTMLElement).render(
   <StrictMode>
     <RouterProvider router={router} />
   </StrictMode>,
diff --git a/apps/yaak-client/package.json b/apps/yaak-client/package.json
index b0ea9a47..ee2c69dd 100644
--- a/apps/yaak-client/package.json
+++ b/apps/yaak-client/package.json
@@ -87,6 +87,8 @@
     "@types/react-syntax-highlighter": "^15.5.13",
     "@types/uuid": "^10.0.0",
     "@types/whatwg-mimetype": "^3.0.2",
+    "@yaakapp-internal/theme": "^1.0.0",
+    "@yaakapp-internal/ui": "^1.0.0",
     "@vitejs/plugin-react": "^4.6.0",
     "autoprefixer": "^10.4.21",
     "decompress": "^4.2.1",
diff --git a/apps/yaak-client/tailwind.config.cjs b/apps/yaak-client/tailwind.config.cjs
index e6423f61..d8800fb8 100644
--- a/apps/yaak-client/tailwind.config.cjs
+++ b/apps/yaak-client/tailwind.config.cjs
@@ -1,146 +1,16 @@
-const plugin = require('tailwindcss/plugin');
-
-const sizes = {
-  '2xs': '1.4rem',
-  xs: '1.8rem',
-  sm: '2.0rem',
-  md: '2.3rem',
-  lg: '2.6rem',
-};
+const sharedConfig = require("@yaakapp-internal/tailwind-config");
 
 /** @type {import('tailwindcss').Config} */
 module.exports = {
-  darkMode: ['class', '[data-resolved-appearance="dark"]'],
+  ...sharedConfig,
   content: [
-    './*.{html,ts,tsx}',
-    './commands/**/*.{ts,tsx}',
-    './components/**/*.{ts,tsx}',
-    './hooks/**/*.{ts,tsx}',
-    './init/**/*.{ts,tsx}',
-    './lib/**/*.{ts,tsx}',
-    './routes/**/*.{ts,tsx}',
-  ],
-  theme: {
-    extend: {
-      keyframes: {
-        blinkRing: {
-          '0%, 49%': { '--tw-ring-color': 'var(--primary)' },
-          '50%, 99%': { '--tw-ring-color': 'transparent' },
-          '100%': { '--tw-ring-color': 'var(--primary)' },
-        },
-      },
-      animation: {
-        blinkRing: 'blinkRing 150ms step-start 400ms infinite',
-      },
-      opacity: {
-        disabled: '0.3',
-      },
-      fontSize: {
-        xs: '0.8rem',
-      },
-      height: sizes,
-      width: sizes,
-      minHeight: sizes,
-      minWidth: sizes,
-      lineHeight: {
-        // HACK: Minus 2 to account for borders inside inputs
-        xs: 'calc(1.75rem - 2px)',
-        sm: 'calc(2.0rem - 2px)',
-        md: 'calc(2.5rem - 2px)',
-      },
-      transitionProperty: {
-        grid: 'grid',
-      },
-    },
-    fontFamily: {
-      mono: [
-        'var(--font-family-editor)',
-        'JetBrains Mono',
-        'ui-monospace',
-        'SFMono-Regular',
-        'Menlo',
-        'Monaco',
-        'Fira Code',
-        'Ubuntu Mono',
-        'Consolas',
-        'Liberation Mono',
-        'Courier New',
-        'DejaVu Sans Mono',
-        'Hack',
-        'monospace',
-      ],
-      sans: [
-        'var(--font-family-interface)',
-        'Inter UI',
-        '-apple-system',
-        'BlinkMacSystemFont',
-        'Segoe UI',
-        'Roboto',
-        'Oxygen-Sans',
-        'Ubuntu',
-        'Cantarell',
-        'Helvetica Neue',
-        'sans-serif',
-        'Apple Color Emoji',
-        'Segoe UI Emoji',
-        'Segoe UI Symbol',
-      ],
-    },
-    fontSize: {
-      '4xs': '0.6rem',
-      '3xs': '0.675rem',
-      '2xs': '0.75rem',
-      xs: '0.8rem',
-      sm: '0.9rem',
-      base: '1rem',
-      lg: '1.12rem',
-      xl: '1.25rem',
-      '2xl': '1.5rem',
-      '3xl': '2rem',
-      '4xl': '2.5rem',
-      '5xl': '3rem',
-      editor: 'var(--editor-font-size)',
-      shrink: '0.8em',
-    },
-    boxShadow: {
-      DEFAULT: '0 1px 3px 0 var(--shadow)',
-      lg: '0 10px 15px -3px var(--shadow)',
-    },
-    colors: {
-      transparent: 'transparent',
-      placeholder: 'var(--textSubtlest)',
-      shadow: 'var(--shadow)',
-      backdrop: 'var(--backdrop)',
-      selection: 'var(--selection)',
-
-      // New theme values
-
-      surface: 'var(--surface)',
-      'surface-highlight': 'var(--surfaceHighlight)',
-      'surface-active': 'var(--surfaceActive)',
-
-      text: 'var(--text)',
-      'text-subtle': 'var(--textSubtle)',
-      'text-subtlest': 'var(--textSubtlest)',
-
-      border: 'var(--border)',
-      'border-subtle': 'var(--borderSubtle)',
-      'border-focus': 'var(--borderFocus)',
-
-      primary: 'var(--primary)',
-      danger: 'var(--danger)',
-      secondary: 'var(--secondary)',
-      success: 'var(--success)',
-      info: 'var(--info)',
-      notice: 'var(--notice)',
-      warning: 'var(--warning)',
-    },
-  },
-  plugins: [
-    require('@tailwindcss/container-queries'),
-    plugin(function ({ addVariant }) {
-      addVariant('hocus', ['&:hover', '&:focus-visible', '&.focus:focus']);
-      addVariant('focus-visible-or-class', ['&:focus-visible', '&.focus:focus']);
-    }),
+    "./*.{html,ts,tsx}",
+    "./commands/**/*.{ts,tsx}",
+    "./components/**/*.{ts,tsx}",
+    "./hooks/**/*.{ts,tsx}",
+    "./init/**/*.{ts,tsx}",
+    "./lib/**/*.{ts,tsx}",
+    "./routes/**/*.{ts,tsx}",
+    "../../packages/ui/src/**/*.{ts,tsx}",
   ],
 };
diff --git a/apps/yaak-client/theme.ts b/apps/yaak-client/theme.ts
index 03957687..6ff7ccff 100644
--- a/apps/yaak-client/theme.ts
+++ b/apps/yaak-client/theme.ts
@@ -1,12 +1,15 @@
-import { listen } from '@tauri-apps/api/event';
-import { getCurrentWebviewWindow } from '@tauri-apps/api/webviewWindow';
-import { setWindowTheme } from '@yaakapp-internal/mac-window';
-import type { ModelPayload } from '@yaakapp-internal/models';
-import { getSettings } from './lib/settings';
-import type { Appearance } from './lib/theme/appearance';
-import { getCSSAppearance, subscribeToPreferredAppearance } from './lib/theme/appearance';
-import { getResolvedTheme } from './lib/theme/themes';
-import { addThemeStylesToDocument, setThemeOnDocument } from './lib/theme/window';
+import { listen } from "@tauri-apps/api/event";
+import { getCurrentWebviewWindow } from "@tauri-apps/api/webviewWindow";
+import { setWindowTheme } from "@yaakapp-internal/mac-window";
+import type { ModelPayload } from "@yaakapp-internal/models";
+import { getSettings } from "./lib/settings";
+import type { Appearance } from "./lib/theme/appearance";
+import {
+  getCSSAppearance,
+  subscribeToPreferredAppearance,
+} from "./lib/theme/appearance";
+import { getResolvedTheme } from "./lib/theme/themes";
+import { applyThemeToDocument } from "@yaakapp-internal/theme";
 
 // NOTE: CSS appearance isn't as accurate as getting it async from the window (next step), but we want
 //  a good appearance guess so we're not waiting too long
@@ -22,15 +25,15 @@ configureTheme().then(
     // need to show it here, after configuring the theme for the first time.
     await getCurrentWebviewWindow().show();
   },
-  (err) => console.log('Failed to configure theme', err),
+  (err) => console.log("Failed to configure theme", err),
 );
 
 // Listen for settings changes, the re-compute theme
-listen<ModelPayload>('model_write', async (event) => {
-  if (event.payload.change.type !== 'upsert') return;
+listen<ModelPayload>("model_write", async (event) => {
+  if (event.payload.change.type !== "upsert") return;
 
   const model = event.payload.model.model;
-  if (model !== 'settings' && model !== 'plugin') return;
+  if (model !== "settings" && model !== "plugin") return;
   await configureTheme();
 }).catch(console.error);
 
@@ -42,8 +45,7 @@ async function configureTheme() {
     settings.themeLight,
     settings.themeDark,
   );
-  addThemeStylesToDocument(theme.active);
-  setThemeOnDocument(theme.active);
+  applyThemeToDocument(theme.active);
   if (theme.active.base.surface != null) {
     setWindowTheme(theme.active.base.surface);
   }
diff --git a/apps/yaak-client/tsconfig.json b/apps/yaak-client/tsconfig.json
index 9add434b..8d760680 100644
--- a/apps/yaak-client/tsconfig.json
+++ b/apps/yaak-client/tsconfig.json
@@ -15,9 +15,16 @@
     "resolveJsonModule": true,
     "isolatedModules": true,
     "noEmit": true,
-    "jsx": "react-jsx"
+    "jsx": "react-jsx",
+    "baseUrl": ".",
+    "paths": {
+      "@yaakapp-internal/theme": ["../../packages/theme/src/index.ts"],
+      "@yaakapp-internal/theme/*": ["../../packages/theme/src/*"],
+      "@yaakapp-internal/ui": ["../../packages/ui/src/index.ts"],
+      "@yaakapp-internal/ui/*": ["../../packages/ui/src/*"],
+    },
   },
   "include": ["."],
   "exclude": ["vite.config.ts"],
-  "references": [{ "path": "./tsconfig.node.json" }]
+  "references": [{ "path": "./tsconfig.node.json" }],
 }
diff --git a/apps/yaak-proxy/index.html b/apps/yaak-proxy/index.html
index 61707262..aed2c7a9 100644
--- a/apps/yaak-proxy/index.html
+++ b/apps/yaak-proxy/index.html
@@ -1,12 +1,27 @@
-<!DOCTYPE html>
+<!doctype html>
 <html lang="en">
-<head>
-  <meta charset="UTF-8" />
-  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
-  <title>Yaak Proxy</title>
-</head>
-<body>
-<div id="root"></div>
-<script type="module" src="/main.tsx"></script>
-</body>
+  <head>
+    <meta charset="UTF-8" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <title>Yaak Proxy</title>
+
+    <style>
+      html,
+      body {
+        background-color: white;
+      }
+
+      @media (prefers-color-scheme: dark) {
+        html,
+        body {
+          background-color: #1b1a29;
+        }
+      }
+    </style>
+  </head>
+  <body class="text-base">
+    <div id="root"></div>
+    <script type="module" src="/theme.ts"></script>
+    <script type="module" src="/main.tsx"></script>
+  </body>
 </html>
diff --git a/apps/yaak-proxy/main.css b/apps/yaak-proxy/main.css
index dc94457c..dff6389f 100644
--- a/apps/yaak-proxy/main.css
+++ b/apps/yaak-proxy/main.css
@@ -1,95 +1,92 @@
-:root {
-  color: #f4efe7;
-  background:
-    radial-gradient(circle at top, rgba(217, 119, 6, 0.35), transparent 45%),
-    linear-gradient(180deg, #18212b 0%, #0f141a 100%);
-  font-family: "IBM Plex Sans", "Segoe UI", sans-serif;
-}
+@tailwind base;
+@tailwind components;
+@tailwind utilities;
 
-* {
-  box-sizing: border-box;
-}
+@layer base {
+  html,
+  body,
+  #root {
+    @apply w-full h-full overflow-hidden text-text bg-surface;
+  }
 
-html,
-body,
-#root {
-  margin: 0;
-  min-height: 100%;
-}
+  :root {
+    --font-family-interface: "";
+    --font-family-editor: "";
+  }
 
-body {
-  min-height: 100vh;
-}
+  :root {
+    font-variant-ligatures: none;
+  }
 
-.app-shell {
-  min-height: 100vh;
-  display: grid;
-  place-items: center;
-  padding: 24px;
-}
+  html[data-platform="linux"] {
+    font-synthesis: none;
+    text-rendering: optimizeLegibility;
+    -webkit-font-smoothing: antialiased;
+    -moz-osx-font-smoothing: grayscale;
+    -webkit-text-size-adjust: 100%;
+  }
 
-.hero-card {
-  width: min(680px, 100%);
-  padding: 40px;
-  border: 1px solid rgba(244, 239, 231, 0.12);
-  border-radius: 28px;
-  background: rgba(9, 12, 16, 0.7);
-  box-shadow: 0 24px 80px rgba(0, 0, 0, 0.35);
-  backdrop-filter: blur(18px);
-}
+  ::selection {
+    @apply bg-selection;
+  }
 
-.eyebrow {
-  margin: 0 0 12px;
-  font-size: 12px;
-  letter-spacing: 0.24em;
-  text-transform: uppercase;
-  color: #f6ad55;
-}
+  :not(a),
+  :not(input):not(textarea),
+  :not(input):not(textarea)::after,
+  :not(input):not(textarea)::before {
+    @apply select-none cursor-default;
+  }
 
-h1 {
-  margin: 0;
-  font-size: clamp(44px, 8vw, 84px);
-  line-height: 0.95;
-}
+  input,
+  textarea {
+    &::placeholder {
+      @apply text-placeholder;
+    }
+  }
 
-.lede {
-  margin: 20px 0 0;
-  max-width: 48ch;
-  font-size: 18px;
-  line-height: 1.6;
-  color: rgba(244, 239, 231, 0.78);
-}
+  a,
+  a[href] * {
+    @apply cursor-pointer !important;
+  }
 
-.controls {
-  margin-top: 28px;
-  display: flex;
-  gap: 12px;
-}
+  table th {
+    @apply text-left;
+  }
 
-.btn {
-  border: 0;
-  border-radius: 10px;
-  padding: 10px 14px;
-  background: #f6ad55;
-  color: #111;
-  font-weight: 700;
-  cursor: pointer;
-}
+  :not(iframe) {
+    &::-webkit-scrollbar,
+    &::-webkit-scrollbar-corner {
+      @apply w-[8px] h-[8px] bg-transparent;
+    }
 
-.btn.ghost {
-  background: rgba(255, 255, 255, 0.12);
-  color: #f4efe7;
-}
+    &::-webkit-scrollbar-track {
+      @apply bg-transparent;
+    }
 
-.btn:disabled {
-  opacity: 0.6;
-  cursor: default;
-}
+    &::-webkit-scrollbar-thumb {
+      @apply bg-text-subtlest rounded-[4px] opacity-20;
+    }
 
-.status {
-  margin-top: 14px;
-  display: flex;
-  gap: 16px;
-  color: rgba(244, 239, 231, 0.88);
-  font-size: 14px;
+    &::-webkit-scrollbar-thumb:hover {
+      @apply opacity-40 !important;
+    }
+  }
+
+  .hide-scrollbars {
+    &::-webkit-scrollbar-corner,
+    &::-webkit-scrollbar {
+      @apply hidden !important;
+    }
+  }
+
+  .rtl {
+    direction: rtl;
+  }
+
+  :root {
+    color-scheme: light dark;
+    --transition-duration: 100ms ease-in-out;
+    --color-white: 255 100% 100%;
+    --color-black: 255 0% 0%;
+  }
 }
diff --git a/apps/yaak-proxy/main.tsx b/apps/yaak-proxy/main.tsx
index def1b0d1..7db63249 100644
--- a/apps/yaak-proxy/main.tsx
+++ b/apps/yaak-proxy/main.tsx
@@ -1,4 +1,5 @@
 import "./main.css";
+import { Button } from "@yaakapp-internal/ui";
 import { invoke } from "@tauri-apps/api/core";
 import { StrictMode } from "react";
 import { useState } from "react";
@@ -45,25 +46,38 @@ function App() {
   }
 
   return (
-    <main className="app-shell">
-      <section className="hero-card">
-        <p className="eyebrow">Monorepo Smoke Test</p>
-        <h1>Yaak Proxy</h1>
-        <p className="lede">
-          This is a minimal proxy app stub running on the new `apps/yaak-proxy`
-          and `crates-tauri/yaak-app-proxy` structure.
-        </p>
-        <div className="controls">
-          <button className="btn" disabled={busy} onClick={startProxy}>
-            Start Proxy
-          </button>
-          <button className="btn ghost" disabled={busy} onClick={stopProxy}>
-            Stop Proxy
-          </button>
-        </div>
-        <div className="status">
-          <span>Status: {status}</span>
-          {port != null ? <span>Port: {port}</span> : null}
+    <main className="h-full w-full overflow-auto p-6">
+      <section className="flex items-start">
+        <div className="flex w-full max-w-xl flex-col gap-4">
+          <div>
+            <h1 className="text-2xl font-semibold text-text">Yaak Proxy</h1>
+            <p className="mt-2 text-sm text-text-subtle">Status: {status}</p>
+            <p className="mt-1 text-sm text-text-subtle">
+              Port: {port ?? "Not running"}
+            </p>
+          </div>
+
+          <div className="flex flex-wrap gap-3">
+            <Button
+              disabled={busy}
+              onClick={startProxy}
+              size="sm"
+              tone="primary"
+            >
+              Start Proxy
+            </Button>
+            <Button
+              disabled={busy}
+              onClick={stopProxy}
+              size="sm"
+              variant="border"
+            >
+              Stop Proxy
+            </Button>
+            <Button size="sm" type="button">
+              Shared Button
+            </Button>
+          </div>
         </div>
       </section>
     </main>
diff --git a/apps/yaak-proxy/package.json b/apps/yaak-proxy/package.json
index 2a11a291..64fd56fd 100644
--- a/apps/yaak-proxy/package.json
+++ b/apps/yaak-proxy/package.json
@@ -9,6 +9,8 @@
     "lint": "tsc --noEmit"
   },
   "dependencies": {
+    "@yaakapp-internal/theme": "^1.0.0",
+    "@yaakapp-internal/ui": "^1.0.0",
     "@tauri-apps/api": "^2.9.1",
     "react": "^19.1.0",
     "react-dom": "^19.1.0"
diff --git a/apps/yaak-proxy/postcss.config.cjs b/apps/yaak-proxy/postcss.config.cjs
new file mode 100644
index 00000000..5b832920
--- /dev/null
+++ b/apps/yaak-proxy/postcss.config.cjs
@@ -0,0 +1,7 @@
+module.exports = {
+  plugins: [
+    require("@tailwindcss/nesting")(require("postcss-nesting")),
+    require("tailwindcss"),
+    require("autoprefixer"),
+  ],
+};
diff --git a/apps/yaak-proxy/tailwind.config.cjs b/apps/yaak-proxy/tailwind.config.cjs
new file mode 100644
index 00000000..6d6eace8
--- /dev/null
+++ b/apps/yaak-proxy/tailwind.config.cjs
@@ -0,0 +1,7 @@
+const sharedConfig = require("@yaakapp-internal/tailwind-config");
+
+/** @type {import('tailwindcss').Config} */
+module.exports = {
+  ...sharedConfig,
+  content: ["./*.{html,ts,tsx}", "../../packages/ui/src/**/*.{ts,tsx}"],
+};
diff --git a/apps/yaak-proxy/theme.ts b/apps/yaak-proxy/theme.ts
new file mode 100644
index 00000000..9a108c6f
--- /dev/null
+++ b/apps/yaak-proxy/theme.ts
@@ -0,0 +1,9 @@
+import {
+  applyThemeToDocument,
+  defaultDarkTheme,
+  platformFromUserAgent,
+  setPlatformOnDocument,
+} from "@yaakapp-internal/theme";
+
+setPlatformOnDocument(platformFromUserAgent(navigator.userAgent));
+applyThemeToDocument(defaultDarkTheme);
diff --git a/apps/yaak-proxy/tsconfig.json b/apps/yaak-proxy/tsconfig.json
index 7ba5265a..c2eba75d 100644
--- a/apps/yaak-proxy/tsconfig.json
+++ b/apps/yaak-proxy/tsconfig.json
@@ -14,9 +14,16 @@
     "resolveJsonModule": true,
     "isolatedModules": true,
     "noEmit": true,
-    "jsx": "react-jsx"
+    "jsx": "react-jsx",
+    "baseUrl": ".",
+    "paths": {
+      "@yaakapp-internal/theme": ["../../packages/theme/src/index.ts"],
+      "@yaakapp-internal/theme/*": ["../../packages/theme/src/*"],
+      "@yaakapp-internal/ui": ["../../packages/ui/src/index.ts"],
+      "@yaakapp-internal/ui/*": ["../../packages/ui/src/*"],
+    },
   },
   "include": ["."],
   "exclude": ["vite.config.ts"],
-  "references": [{ "path": "./tsconfig.node.json" }]
+  "references": [{ "path": "./tsconfig.node.json" }],
 }
diff --git a/package-lock.json b/package-lock.json
index a308f33d..cedbb42b 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -8,6 +8,9 @@
       "name": "yaak-monorepo",
       "version": "0.0.0",
       "workspaces": [
+        "packages/ui",
+        "packages/theme",
+        "packages/tailwind-config",
         "packages/common-lib",
         "packages/plugin-runtime",
         "packages/plugin-runtime-types",
@@ -167,6 +170,8 @@
         "@types/uuid": "^10.0.0",
         "@types/whatwg-mimetype": "^3.0.2",
         "@vitejs/plugin-react": "^4.6.0",
+        "@yaakapp-internal/theme": "^1.0.0",
+        "@yaakapp-internal/ui": "^1.0.0",
         "autoprefixer": "^10.4.21",
         "decompress": "^4.2.1",
         "internal-ip": "^8.0.0",
@@ -220,6 +225,8 @@
       "version": "1.0.0",
       "dependencies": {
         "@tauri-apps/api": "^2.9.1",
+        "@yaakapp-internal/theme": "^1.0.0",
+        "@yaakapp-internal/ui": "^1.0.0",
         "react": "^19.1.0",
         "react-dom": "^19.1.0"
       },
@@ -305,7 +312,6 @@
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       "resolved": "https://registry.npmjs.org/@alloc/quick-lru/-/quick-lru-5.2.0.tgz",
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-      "dev": true,
       "license": "MIT",
       "engines": {
         "node": ">=10"
@@ -1666,7 +1672,6 @@
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-      "devOptional": true,
       "license": "MIT",
       "dependencies": {
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@@ -1688,7 +1693,6 @@
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       "resolved": "https://registry.npmjs.org/@jridgewell/resolve-uri/-/resolve-uri-3.1.2.tgz",
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-      "devOptional": true,
       "license": "MIT",
       "engines": {
         "node": ">=6.0.0"
@@ -1704,7 +1708,6 @@
       "version": "0.3.31",
       "resolved": "https://registry.npmjs.org/@jridgewell/trace-mapping/-/trace-mapping-0.3.31.tgz",
       "integrity": "sha512-zzNR+SdQSDJzc8joaeP8QQoCQr8NuYx2dIIytl1QeBEZHJ9uW6hebsrYgbz8hJwUQao3TWCMtmfV8Nu1twOLAw==",
-      "devOptional": true,
       "license": "MIT",
       "dependencies": {
         "@jridgewell/resolve-uri": "^3.1.0",
@@ -3255,7 +3258,6 @@
       "version": "0.1.1",
       "resolved": "https://registry.npmjs.org/@tailwindcss/container-queries/-/container-queries-0.1.1.tgz",
       "integrity": "sha512-p18dswChx6WnTSaJCSGx6lTmrGzNNvm2FtXmiO6AuA1V4U5REyoqwmT6kgAsIMdjo07QdAfYXHJ4hnMtfHzWgA==",
-      "dev": true,
       "license": "MIT",
       "peerDependencies": {
         "tailwindcss": ">=3.2.0"
@@ -4435,6 +4437,10 @@
       "resolved": "crates/yaak-sync",
       "link": true
     },
+    "node_modules/@yaakapp-internal/tailwind-config": {
+      "resolved": "packages/tailwind-config",
+      "link": true
+    },
     "node_modules/@yaakapp-internal/tauri-client": {
       "resolved": "crates-tauri/yaak-app-client",
       "link": true
@@ -4447,6 +4453,14 @@
       "resolved": "crates/yaak-templates",
       "link": true
     },
+    "node_modules/@yaakapp-internal/theme": {
+      "resolved": "packages/theme",
+      "link": true
+    },
+    "node_modules/@yaakapp-internal/ui": {
+      "resolved": "packages/ui",
+      "link": true
+    },
     "node_modules/@yaakapp-internal/ws": {
       "resolved": "crates/yaak-ws",
       "link": true
@@ -4755,14 +4769,12 @@
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       "resolved": "https://registry.npmjs.org/any-promise/-/any-promise-1.3.0.tgz",
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-      "dev": true,
       "license": "MIT"
     },
     "node_modules/anymatch": {
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       "resolved": "https://registry.npmjs.org/anymatch/-/anymatch-3.1.3.tgz",
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-      "dev": true,
       "license": "ISC",
       "dependencies": {
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@@ -4776,7 +4788,6 @@
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-      "dev": true,
       "license": "MIT",
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@@ -4789,7 +4800,6 @@
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-      "dev": true,
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-      "dev": true,
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@@ -5274,7 +5283,6 @@
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-      "dev": true,
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-      "dev": true,
       "license": "MIT",
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@@ -6087,7 +6094,6 @@
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-      "dev": true,
       "license": "MIT",
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@@ -6496,7 +6502,6 @@
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-      "dev": true,
       "license": "Apache-2.0"
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@@ -6541,7 +6546,6 @@
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-      "dev": true,
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     "node_modules/dot-case": {
@@ -6908,7 +6912,7 @@
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-      "dev": true,
+      "devOptional": true,
       "hasInstallScript": true,
       "license": "MIT",
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@@ -7297,7 +7301,6 @@
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       "resolved": "https://registry.npmjs.org/fdir/-/fdir-6.5.0.tgz",
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-      "dev": true,
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@@ -7575,7 +7578,6 @@
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@@ -7752,7 +7754,7 @@
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-      "dev": true,
+      "devOptional": true,
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@@ -8597,7 +8599,6 @@
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@@ -8638,7 +8639,6 @@
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       "integrity": "sha512-udgsAY+fTnvv7kI7aaxbqwWNb0AHiB0qBO89PZKPkoTmGOgdbrHDKD+0B2X4uTfJ/FT1R09r9gTsjUjNJotuog==",
-      "dev": true,
       "license": "MIT",
       "engines": {
         "node": ">=0.10.0"
@@ -12812,7 +12796,6 @@
       "version": "3.6.0",
       "resolved": "https://registry.npmjs.org/readdirp/-/readdirp-3.6.0.tgz",
       "integrity": "sha512-hOS089on8RduqdbhvQ5Z37A0ESjsqz6qnRcffsMU3495FuTdqSm+7bhJ29JvIOsBDEEnan5DPu9t3To9VRlMzA==",
-      "dev": true,
       "license": "MIT",
       "dependencies": {
         "picomatch": "^2.2.1"
@@ -12825,7 +12808,6 @@
       "version": "2.3.1",
       "resolved": "https://registry.npmjs.org/picomatch/-/picomatch-2.3.1.tgz",
       "integrity": "sha512-JU3teHTNjmE2VCGFzuY8EXzCDVwEqB2a8fsIvwaStHhAWJEeVd1o1QD80CU6+ZdEXXSLbSsuLwJjkCBWqRQUVA==",
-      "dev": true,
       "license": "MIT",
       "engines": {
         "node": ">=8.6"
@@ -13060,7 +13042,6 @@
       "version": "1.22.11",
       "resolved": "https://registry.npmjs.org/resolve/-/resolve-1.22.11.tgz",
       "integrity": "sha512-RfqAvLnMl313r7c9oclB1HhUEAezcpLjz95wFH4LVuhk9JF/r22qmVP9AMmOU4vMX7Q8pN8jwNg/CSpdFnMjTQ==",
-      "dev": true,
       "license": "MIT",
       "dependencies": {
         "is-core-module": "^2.16.1",
@@ -13090,7 +13071,7 @@
       "version": "1.0.0",
       "resolved": "https://registry.npmjs.org/resolve-pkg-maps/-/resolve-pkg-maps-1.0.0.tgz",
       "integrity": "sha512-seS2Tj26TBVOC2NIc2rOe2y2ZO7efxITtLZcGSOnHHNOQ7CkiUBfw0Iw2ck6xkIhPwLhKNLS8BO+hEpngQlqzw==",
-      "dev": true,
+      "devOptional": true,
       "license": "MIT",
       "funding": {
         "url": "https://github.com/privatenumber/resolve-pkg-maps?sponsor=1"
@@ -13830,7 +13811,6 @@
       "version": "1.2.1",
       "resolved": "https://registry.npmjs.org/source-map-js/-/source-map-js-1.2.1.tgz",
       "integrity": "sha512-UXWMKhLOwVKb728IUtQPXxfYU+usdybtUrK/8uGE8CQMvrhOpwvzDBwj0QhSL7MQc7vIsISBG8VQ8+IDQxpfQA==",
-      "dev": true,
       "license": "BSD-3-Clause",
       "engines": {
         "node": ">=0.10.0"
@@ -14296,7 +14276,6 @@
       "version": "3.35.1",
       "resolved": "https://registry.npmjs.org/sucrase/-/sucrase-3.35.1.tgz",
       "integrity": "sha512-DhuTmvZWux4H1UOnWMB3sk0sbaCVOoQZjv8u1rDoTV0HTdGem9hkAZtl4JZy8P2z4Bg0nT+YMeOFyVr4zcG5Tw==",
-      "dev": true,
       "license": "MIT",
       "dependencies": {
         "@jridgewell/gen-mapping": "^0.3.2",
@@ -14319,7 +14298,6 @@
       "version": "4.1.1",
       "resolved": "https://registry.npmjs.org/commander/-/commander-4.1.1.tgz",
       "integrity": "sha512-NOKm8xhkzAjzFx8B2v5OAHT+u5pRQc2UCa2Vq9jYL/31o2wi9mxBA7LIFs3sV5VSC49z6pEhfbMULvShKj26WA==",
-      "dev": true,
       "license": "MIT",
       "engines": {
         "node": ">= 6"
@@ -14360,7 +14338,6 @@
       "version": "1.0.0",
       "resolved": "https://registry.npmjs.org/supports-preserve-symlinks-flag/-/supports-preserve-symlinks-flag-1.0.0.tgz",
       "integrity": "sha512-ot0WnXS9fgdkgIcePe6RHNk1WA8+muPa6cSjeR3V8K27q9BB1rTE3R1p7Hv0z1ZyAc8s6Vvv8DIyWf681MAt0w==",
-      "dev": true,
       "license": "MIT",
       "engines": {
         "node": ">= 0.4"
@@ -14563,7 +14540,6 @@
       "version": "3.4.19",
       "resolved": "https://registry.npmjs.org/tailwindcss/-/tailwindcss-3.4.19.tgz",
       "integrity": "sha512-3ofp+LL8E+pK/JuPLPggVAIaEuhvIz4qNcf3nA1Xn2o/7fb7s/TYpHhwGDv1ZU3PkBluUVaF8PyCHcm48cKLWQ==",
-      "dev": true,
       "license": "MIT",
       "dependencies": {
         "@alloc/quick-lru": "^5.2.0",
@@ -14601,7 +14577,6 @@
       "version": "6.0.2",
       "resolved": "https://registry.npmjs.org/glob-parent/-/glob-parent-6.0.2.tgz",
       "integrity": "sha512-XxwI8EOhVQgWp6iDL+3b0r86f4d6AX6zSU55HfB4ydCEuXLXc5FcYeOu+nnGftS4TEju/11rt4KJPTMgbfmv4A==",
-      "dev": true,
       "license": "ISC",
       "dependencies": {
         "is-glob": "^4.0.3"
@@ -14614,7 +14589,6 @@
       "version": "6.2.0",
       "resolved": "https://registry.npmjs.org/postcss-nested/-/postcss-nested-6.2.0.tgz",
       "integrity": "sha512-HQbt28KulC5AJzG+cZtj9kvKB93CFCdLvog1WFLf1D+xmMvPGlBstkpTEZfK5+AN9hfJocyBFCNiqyS48bpgzQ==",
-      "dev": true,
       "funding": [
         {
           "type": "opencollective",
@@ -14659,7 +14633,6 @@
       "version": "3.3.1",
       "resolved": "https://registry.npmjs.org/thenify/-/thenify-3.3.1.tgz",
       "integrity": "sha512-RVZSIV5IG10Hk3enotrhvz0T9em6cyHBLkH/YAZuKqd8hRkKhSfCGIcP2KUY0EPxndzANBmNllzWPwak+bheSw==",
-      "dev": true,
       "license": "MIT",
       "dependencies": {
         "any-promise": "^1.0.0"
@@ -14669,7 +14642,6 @@
       "version": "1.6.0",
       "resolved": "https://registry.npmjs.org/thenify-all/-/thenify-all-1.6.0.tgz",
       "integrity": "sha512-RNxQH/qI8/t3thXJDwcstUO4zeqo64+Uy/+sNVRBx4Xn2OX+OZ9oP+iJnNFqplFra2ZUVeKCSa2oVWi3T4uVmA==",
-      "dev": true,
       "license": "MIT",
       "dependencies": {
         "thenify": ">= 3.1.0 < 4"
@@ -14740,7 +14712,6 @@
       "version": "0.2.15",
       "resolved": "https://registry.npmjs.org/tinyglobby/-/tinyglobby-0.2.15.tgz",
       "integrity": "sha512-j2Zq4NyQYG5XMST4cbs02Ak8iJUdxRM0XI5QyxXuZOzKOINmWurp3smXu3y5wDcJrptwpSjgXHzIQxR0omXljQ==",
-      "dev": true,
       "license": "MIT",
       "dependencies": {
         "fdir": "^6.5.0",
@@ -14871,7 +14842,6 @@
       "version": "0.1.13",
       "resolved": "https://registry.npmjs.org/ts-interface-checker/-/ts-interface-checker-0.1.13.tgz",
       "integrity": "sha512-Y/arvbn+rrz3JCKl9C4kVNfTfSm2/mEp5FSz5EsZSANGPSlQrpRI5M4PKF+mJnE52jOO90PnPSc3Ur3bTQw0gA==",
-      "dev": true,
       "license": "Apache-2.0"
     },
     "node_modules/tslib": {
@@ -14884,7 +14854,7 @@
       "version": "4.21.0",
       "resolved": "https://registry.npmjs.org/tsx/-/tsx-4.21.0.tgz",
       "integrity": "sha512-5C1sg4USs1lfG0GFb2RLXsdpXqBSEhAaA/0kPL01wxzpMqLILNxIxIOKiILz+cdg/pLnOUxFYOR5yhHU666wbw==",
-      "dev": true,
+      "devOptional": true,
       "license": "MIT",
       "dependencies": {
         "esbuild": "~0.27.0",
@@ -15280,7 +15250,6 @@
       "version": "1.0.2",
       "resolved": "https://registry.npmjs.org/util-deprecate/-/util-deprecate-1.0.2.tgz",
       "integrity": "sha512-EPD5q1uXyFxJpCrLnCc1nHnq3gOa6DZBocAIiI2TaSCA7VCJ1UJDMagCzIkXNsUYfD1daK//LTEQ8xiIbrHtcw==",
-      "dev": true,
       "license": "MIT"
     },
     "node_modules/uuid": {
@@ -16165,6 +16134,34 @@
         "undici-types": "~7.16.0"
       }
     },
+    "packages/tailwind-config": {
+      "name": "@yaakapp-internal/tailwind-config",
+      "version": "1.0.0",
+      "dependencies": {
+        "@tailwindcss/container-queries": "^0.1.1",
+        "tailwindcss": "^3.4.17"
+      }
+    },
+    "packages/theme": {
+      "version": "1.0.0",
+      "dependencies": {
+        "@tauri-apps/api": "^2.9.1",
+        "@yaakapp-internal/plugins": "^1.0.0",
+        "parse-color": "^1.0.0"
+      }
+    },
+    "packages/ui": {
+      "name": "@yaakapp-internal/ui",
+      "version": "1.0.0",
+      "dependencies": {
+        "react": "^19.1.0",
+        "react-dom": "^19.1.0"
+      },
+      "peerDependencies": {
+        "react": "^19.1.0",
+        "react-dom": "^19.1.0"
+      }
+    },
     "plugins-external/faker": {
       "name": "@yaak/faker",
       "version": "1.1.1",
diff --git a/package.json b/package.json
index f758d6fb..3de33e94 100644
--- a/package.json
+++ b/package.json
@@ -7,6 +7,9 @@
     "url": "git+https://github.com/mountain-loop/yaak.git"
   },
   "workspaces": [
+    "packages/ui",
+    "packages/theme",
+    "packages/tailwind-config",
     "packages/common-lib",
     "packages/plugin-runtime",
     "packages/plugin-runtime-types",
diff --git a/packages/tailwind-config/index.cjs b/packages/tailwind-config/index.cjs
new file mode 100644
index 00000000..8622f021
--- /dev/null
+++ b/packages/tailwind-config/index.cjs
@@ -0,0 +1,136 @@
+const plugin = require("tailwindcss/plugin");
+
+const sizes = {
+  "2xs": "1.4rem",
+  xs: "1.8rem",
+  sm: "2.0rem",
+  md: "2.3rem",
+  lg: "2.6rem",
+};
+
+/** @type {import('tailwindcss').Config} */
+module.exports = {
+  darkMode: ["class", '[data-resolved-appearance="dark"]'],
+  theme: {
+    extend: {
+      keyframes: {
+        blinkRing: {
+          "0%, 49%": { "--tw-ring-color": "var(--primary)" },
+          "50%, 99%": { "--tw-ring-color": "transparent" },
+          "100%": { "--tw-ring-color": "var(--primary)" },
+        },
+      },
+      animation: {
+        blinkRing: "blinkRing 150ms step-start 400ms infinite",
+      },
+      opacity: {
+        disabled: "0.3",
+      },
+      fontSize: {
+        xs: "0.8rem",
+      },
+      height: sizes,
+      width: sizes,
+      minHeight: sizes,
+      minWidth: sizes,
+      lineHeight: {
+        // HACK: Minus 2 to account for borders inside inputs
+        xs: "calc(1.75rem - 2px)",
+        sm: "calc(2.0rem - 2px)",
+        md: "calc(2.5rem - 2px)",
+      },
+      transitionProperty: {
+        grid: "grid",
+      },
+    },
+    fontFamily: {
+      mono: [
+        "var(--font-family-editor)",
+        "JetBrains Mono",
+        "ui-monospace",
+        "SFMono-Regular",
+        "Menlo",
+        "Monaco",
+        "Fira Code",
+        "Ubuntu Mono",
+        "Consolas",
+        "Liberation Mono",
+        "Courier New",
+        "DejaVu Sans Mono",
+        "Hack",
+        "monospace",
+      ],
+      sans: [
+        "var(--font-family-interface)",
+        "Inter UI",
+        "-apple-system",
+        "BlinkMacSystemFont",
+        "Segoe UI",
+        "Roboto",
+        "Oxygen-Sans",
+        "Ubuntu",
+        "Cantarell",
+        "Helvetica Neue",
+        "sans-serif",
+        "Apple Color Emoji",
+        "Segoe UI Emoji",
+        "Segoe UI Symbol",
+      ],
+    },
+    fontSize: {
+      "4xs": "0.6rem",
+      "3xs": "0.675rem",
+      "2xs": "0.75rem",
+      xs: "0.8rem",
+      sm: "0.9rem",
+      base: "1rem",
+      lg: "1.12rem",
+      xl: "1.25rem",
+      "2xl": "1.5rem",
+      "3xl": "2rem",
+      "4xl": "2.5rem",
+      "5xl": "3rem",
+      editor: "var(--editor-font-size)",
+      shrink: "0.8em",
+    },
+    boxShadow: {
+      DEFAULT: "0 1px 3px 0 var(--shadow)",
+      lg: "0 10px 15px -3px var(--shadow)",
+    },
+    colors: {
+      transparent: "transparent",
+      placeholder: "var(--textSubtlest)",
+      shadow: "var(--shadow)",
+      backdrop: "var(--backdrop)",
+      selection: "var(--selection)",
+
+      // New theme values
+      surface: "var(--surface)",
+      "surface-highlight": "var(--surfaceHighlight)",
+      "surface-active": "var(--surfaceActive)",
+      text: "var(--text)",
+      "text-subtle": "var(--textSubtle)",
+      "text-subtlest": "var(--textSubtlest)",
+      border: "var(--border)",
+      "border-subtle": "var(--borderSubtle)",
+      "border-focus": "var(--borderFocus)",
+      primary: "var(--primary)",
+      danger: "var(--danger)",
+      secondary: "var(--secondary)",
+      success: "var(--success)",
+      info: "var(--info)",
+      notice: "var(--notice)",
+      warning: "var(--warning)",
+    },
+  },
+  plugins: [
+    require("@tailwindcss/container-queries"),
+    plugin(function ({ addVariant }) {
+      addVariant("hocus", ["&:hover", "&:focus-visible", "&.focus:focus"]);
+      addVariant("focus-visible-or-class", [
+        "&:focus-visible",
+        "&.focus:focus",
+      ]);
+    }),
+  ],
+};
diff --git a/packages/tailwind-config/index.d.ts b/packages/tailwind-config/index.d.ts
new file mode 100644
index 00000000..3f71c5dd
--- /dev/null
+++ b/packages/tailwind-config/index.d.ts
@@ -0,0 +1,5 @@
+import type { Config } from "tailwindcss";
+
+declare const config: Config;
+
+export = config;
diff --git a/packages/tailwind-config/package.json b/packages/tailwind-config/package.json
new file mode 100644
index 00000000..e22bb464
--- /dev/null
+++ b/packages/tailwind-config/package.json
@@ -0,0 +1,11 @@
+{
+  "name": "@yaakapp-internal/tailwind-config",
+  "private": true,
+  "version": "1.0.0",
+  "main": "index.cjs",
+  "types": "index.d.ts",
+  "dependencies": {
+    "@tailwindcss/container-queries": "^0.1.1",
+    "tailwindcss": "^3.4.17"
+  }
+}
diff --git a/packages/theme/package.json b/packages/theme/package.json
new file mode 100644
index 00000000..b59c778a
--- /dev/null
+++ b/packages/theme/package.json
@@ -0,0 +1,13 @@
+{
+  "name": "@yaakapp-internal/theme",
+  "private": true,
+  "version": "1.0.0",
+  "type": "module",
+  "main": "src/index.ts",
+  "types": "src/index.ts",
+  "dependencies": {
+    "@tauri-apps/api": "^2.9.1",
+    "@yaakapp-internal/plugins": "^1.0.0",
+    "parse-color": "^1.0.0"
+  }
+}
diff --git a/packages/theme/src/appearance.ts b/packages/theme/src/appearance.ts
new file mode 100644
index 00000000..9e5193af
--- /dev/null
+++ b/packages/theme/src/appearance.ts
@@ -0,0 +1,44 @@
+import { getCurrentWebviewWindow } from "@tauri-apps/api/webviewWindow";
+
+export type Appearance = "light" | "dark";
+
+export function getCSSAppearance(): Appearance {
+  return window.matchMedia("(prefers-color-scheme: dark)").matches ? "dark" : "light";
+}
+
+export async function getWindowAppearance(): Promise<Appearance> {
+  const appearance = await getCurrentWebviewWindow().theme();
+  return appearance ?? getCSSAppearance();
+}
+
+export function subscribeToWindowAppearanceChange(
+  cb: (appearance: Appearance) => void,
+): () => void {
+  const container = {
+    unsubscribe: () => {},
+  };
+
+  getCurrentWebviewWindow()
+    .onThemeChanged((theme) => {
+      cb(theme.payload);
+    })
+    .then((listener) => {
+      container.unsubscribe = listener;
+    });
+
+  return () => container.unsubscribe();
+}
+
+export function resolveAppearance(
+  preferredAppearance: Appearance,
+  appearanceSetting: string,
+): Appearance {
+  const appearance = appearanceSetting === "system" ? preferredAppearance : appearanceSetting;
+  return appearance === "dark" ? "dark" : "light";
+}
+
+export function subscribeToPreferredAppearance(cb: (appearance: Appearance) => void) {
+  cb(getCSSAppearance());
+  getWindowAppearance().then(cb);
+  subscribeToWindowAppearanceChange(cb);
+}
diff --git a/packages/theme/src/defaultThemes.ts b/packages/theme/src/defaultThemes.ts
new file mode 100644
index 00000000..439871be
--- /dev/null
+++ b/packages/theme/src/defaultThemes.ts
@@ -0,0 +1,76 @@
+import type { Theme } from "@yaakapp-internal/plugins";
+
+export const defaultDarkTheme: Theme = {
+  id: "yaak-dark",
+  label: "Yaak",
+  dark: true,
+  base: {
+    surface: "hsl(244,23%,14%)",
+    surfaceHighlight: "hsl(244,23%,20%)",
+    text: "hsl(245,23%,85%)",
+    textSubtle: "hsl(245,18%,58%)",
+    textSubtlest: "hsl(245,18%,45%)",
+    border: "hsl(244,23%,25%)",
+    primary: "hsl(266,100%,79%)",
+    secondary: "hsl(245,23%,60%)",
+    info: "hsl(206,100%,63%)",
+    success: "hsl(150,99%,44%)",
+    notice: "hsl(48,80%,63%)",
+    warning: "hsl(28,100%,61%)",
+    danger: "hsl(342,90%,68%)",
+  },
+  components: {
+    button: {
+      primary: "hsl(266,100%,71.1%)",
+      secondary: "hsl(244,23%,54%)",
+      info: "hsl(206,100%,56.7%)",
+      success: "hsl(150,99%,37.4%)",
+      notice: "hsl(48,80%,50.4%)",
+      warning: "hsl(28,100%,54.9%)",
+      danger: "hsl(342,90%,61.2%)",
+    },
+    dialog: {
+      border: "hsl(244,23%,24%)",
+    },
+    sidebar: {
+      surface: "hsl(243,23%,16%)",
+      border: "hsl(244,23%,22%)",
+    },
+    responsePane: {
+      surface: "hsl(243,23%,16%)",
+      border: "hsl(246,23%,23%)",
+    },
+    appHeader: {
+      surface: "hsl(244,23%,12%)",
+      border: "hsl(244,23%,21%)",
+    },
+  },
+};
+
+export const defaultLightTheme: Theme = {
+  id: "yaak-light",
+  label: "Yaak",
+  dark: false,
+  base: {
+    surface: "hsl(0,0%,100%)",
+    surfaceHighlight: "hsl(218,24%,87%)",
+    text: "hsl(217,24%,10%)",
+    textSubtle: "hsl(217,24%,40%)",
+    textSubtlest: "hsl(217,24%,58%)",
+    border: "hsl(217,22%,90%)",
+    primary: "hsl(266,100%,60%)",
+    secondary: "hsl(220,24%,50%)",
+    info: "hsl(206,100%,40%)",
+    success: "hsl(139,66%,34%)",
+    notice: "hsl(45,100%,34%)",
+    warning: "hsl(30,100%,36%)",
+    danger: "hsl(335,75%,48%)",
+  },
+  components: {
+    sidebar: {
+      surface: "hsl(220,20%,98%)",
+      border: "hsl(217,22%,88%)",
+      surfaceHighlight: "hsl(217,25%,90%)",
+    },
+  },
+};
diff --git a/packages/theme/src/index.ts b/packages/theme/src/index.ts
new file mode 100644
index 00000000..25455314
--- /dev/null
+++ b/packages/theme/src/index.ts
@@ -0,0 +1,26 @@
+export type { Appearance } from "./appearance";
+export {
+  getCSSAppearance,
+  getWindowAppearance,
+  resolveAppearance,
+  subscribeToPreferredAppearance,
+  subscribeToWindowAppearanceChange,
+} from "./appearance";
+export { defaultDarkTheme, defaultLightTheme } from "./defaultThemes";
+export { YaakColor } from "./yaakColor";
+export type {
+  DocumentPlatform,
+  YaakColorKey,
+  YaakColors,
+  YaakTheme,
+} from "./window";
+export {
+  addThemeStylesToDocument,
+  applyThemeToDocument,
+  completeTheme,
+  getThemeCSS,
+  indent,
+  platformFromUserAgent,
+  setThemeOnDocument,
+  setPlatformOnDocument,
+} from "./window";
diff --git a/packages/theme/src/window.ts b/packages/theme/src/window.ts
new file mode 100644
index 00000000..9d429f53
--- /dev/null
+++ b/packages/theme/src/window.ts
@@ -0,0 +1,430 @@
+import type { Theme, ThemeComponentColors } from "@yaakapp-internal/plugins";
+import { defaultDarkTheme, defaultLightTheme } from "./defaultThemes";
+import { YaakColor } from "./yaakColor";
+
+export type YaakColors = {
+  surface: YaakColor;
+  surfaceHighlight?: YaakColor;
+  surfaceActive?: YaakColor;
+  text: YaakColor;
+  textSubtle?: YaakColor;
+  textSubtlest?: YaakColor;
+  border?: YaakColor;
+  borderSubtle?: YaakColor;
+  borderFocus?: YaakColor;
+  shadow?: YaakColor;
+  backdrop?: YaakColor;
+  selection?: YaakColor;
+  primary?: YaakColor;
+  secondary?: YaakColor;
+  info?: YaakColor;
+  success?: YaakColor;
+  notice?: YaakColor;
+  warning?: YaakColor;
+  danger?: YaakColor;
+};
+
+export type YaakTheme = {
+  id: string;
+  name: string;
+  base: YaakColors;
+  components?: Partial<{
+    dialog: Partial<YaakColors>;
+    menu: Partial<YaakColors>;
+    toast: Partial<YaakColors>;
+    sidebar: Partial<YaakColors>;
+    responsePane: Partial<YaakColors>;
+    appHeader: Partial<YaakColors>;
+    button: Partial<YaakColors>;
+    banner: Partial<YaakColors>;
+    templateTag: Partial<YaakColors>;
+    urlBar: Partial<YaakColors>;
+    editor: Partial<YaakColors>;
+    input: Partial<YaakColors>;
+  }>;
+};
+
+export type YaakColorKey = keyof ThemeComponentColors;
+export type DocumentPlatform = "linux" | "macos" | "windows" | "unknown";
+
+type ComponentName = keyof NonNullable<YaakTheme["components"]>;
+type CSSVariables = Record<YaakColorKey, string | undefined>;
+
+function themeVariables(
+  theme: Theme,
+  component?: ComponentName,
+  base?: CSSVariables,
+): CSSVariables | null {
+  const cmp =
+    component == null
+      ? theme.base
+      : (theme.components?.[component] ?? ({} as ThemeComponentColors));
+  const color = (value: string | undefined) => yc(theme, value);
+  const vars: CSSVariables = {
+    surface: cmp.surface,
+    surfaceHighlight:
+      cmp.surfaceHighlight ?? color(cmp.surface)?.lift(0.06).css(),
+    surfaceActive:
+      cmp.surfaceActive ??
+      color(cmp.primary)?.lower(0.2).translucify(0.8).css(),
+    backdrop:
+      cmp.backdrop ?? color(cmp.surface)?.lower(0.2).translucify(0.2).css(),
+    selection:
+      cmp.selection ?? color(cmp.primary)?.lower(0.1).translucify(0.7).css(),
+    border: cmp.border ?? color(cmp.surface)?.lift(0.11)?.css(),
+    borderSubtle: cmp.borderSubtle ?? color(cmp.border)?.lower(0.06)?.css(),
+    borderFocus: color(cmp.info)?.translucify(0.5)?.css(),
+    text: cmp.text,
+    textSubtle: cmp.textSubtle ?? color(cmp.text)?.lower(0.2)?.css(),
+    textSubtlest: cmp.textSubtlest ?? color(cmp.text)?.lower(0.3)?.css(),
+    shadow:
+      cmp.shadow ??
+      YaakColor.black()
+        .translucify(theme.dark ? 0.7 : 0.93)
+        .css(),
+    primary: cmp.primary,
+    secondary: cmp.secondary,
+    info: cmp.info,
+    success: cmp.success,
+    notice: cmp.notice,
+    warning: cmp.warning,
+    danger: cmp.danger,
+  };
+
+  for (const [key, value] of Object.entries(vars)) {
+    if (!value && base?.[key as YaakColorKey]) {
+      vars[key as YaakColorKey] = base[key as YaakColorKey];
+    }
+  }
+
+  return vars;
+}
+
+function templateTagColorVariables(
+  color: YaakColor | null,
+): Partial<CSSVariables> {
+  if (color == null) return {};
+
+  return {
+    text: color.lift(0.7).css(),
+    textSubtle: color.lift(0.4).css(),
+    textSubtlest: color.css(),
+    surface: color.lower(0.2).translucify(0.8).css(),
+    border: color.translucify(0.6).css(),
+    borderSubtle: color.translucify(0.8).css(),
+    surfaceHighlight: color.lower(0.1).translucify(0.7).css(),
+  };
+}
+
+function toastColorVariables(color: YaakColor | null): Partial<CSSVariables> {
+  if (color == null) return {};
+
+  return {
+    text: color.lift(0.8).css(),
+    textSubtle: color.lift(0.8).translucify(0.3).css(),
+    surface: color.translucify(0.9).css(),
+    surfaceHighlight: color.translucify(0.8).css(),
+    border: color.lift(0.3).translucify(0.6).css(),
+  };
+}
+
+function bannerColorVariables(color: YaakColor | null): Partial<CSSVariables> {
+  if (color == null) return {};
+
+  return {
+    text: color.lift(0.8).css(),
+    textSubtle: color.translucify(0.3).css(),
+    textSubtlest: color.translucify(0.6).css(),
+    surface: color.translucify(0.95).css(),
+    border: color.lift(0.3).translucify(0.8).css(),
+  };
+}
+
+function buttonSolidColorVariables(
+  color: YaakColor | null,
+  isDefault = false,
+): Partial<CSSVariables> {
+  if (color == null) return {};
+
+  const theme: Partial<ThemeComponentColors> = {
+    text: "white",
+    surface: color.lower(0.3).css(),
+    surfaceHighlight: color.lower(0.1).css(),
+    border: color.css(),
+  };
+
+  if (isDefault) {
+    theme.text = undefined;
+    theme.surface = undefined;
+    theme.surfaceHighlight = color.lift(0.08).css();
+  }
+
+  return theme;
+}
+
+function buttonBorderColorVariables(
+  color: YaakColor | null,
+  isDefault = false,
+): Partial<CSSVariables> {
+  if (color == null) return {};
+
+  const vars: Partial<CSSVariables> = {
+    text: color.lift(0.8).css(),
+    textSubtle: color.lift(0.55).css(),
+    textSubtlest: color.lift(0.4).translucify(0.6).css(),
+    surfaceHighlight: color.translucify(0.8).css(),
+    borderSubtle: color.translucify(0.5).css(),
+    border: color.translucify(0.3).css(),
+  };
+
+  if (isDefault) {
+    vars.borderSubtle = color.lift(0.28).css();
+    vars.border = color.lift(0.5).css();
+  }
+
+  return vars;
+}
+
+function variablesToCSS(
+  selector: string | null,
+  vars: Partial<CSSVariables> | null,
+): string | null {
+  if (vars == null) return null;
+
+  const css = Object.entries(vars)
+    .filter(([, value]) => value)
+    .map(([name, value]) => `--${name}: ${value};`)
+    .join("\n");
+
+  return selector == null ? css : `${selector} {\n${indent(css)}\n}`;
+}
+
+function componentCSS(theme: Theme, component: ComponentName): string | null {
+  if (theme.components == null) return null;
+  return variablesToCSS(
+    `.x-theme-${component}`,
+    themeVariables(theme, component),
+  );
+}
+
+function buttonCSS(
+  theme: Theme,
+  colorKey: YaakColorKey,
+  colors?: ThemeComponentColors,
+): string | null {
+  const color = yc(theme, colors?.[colorKey]);
+  if (color == null) return null;
+
+  return [
+    variablesToCSS(
+      `.x-theme-button--solid--${colorKey}`,
+      buttonSolidColorVariables(color),
+    ),
+    variablesToCSS(
+      `.x-theme-button--border--${colorKey}`,
+      buttonBorderColorVariables(color),
+    ),
+  ].join("\n\n");
+}
+
+function bannerCSS(
+  theme: Theme,
+  colorKey: YaakColorKey,
+  colors?: ThemeComponentColors,
+): string | null {
+  const color = yc(theme, colors?.[colorKey]);
+  if (color == null) return null;
+
+  return variablesToCSS(
+    `.x-theme-banner--${colorKey}`,
+    bannerColorVariables(color),
+  );
+}
+
+function toastCSS(
+  theme: Theme,
+  colorKey: YaakColorKey,
+  colors?: ThemeComponentColors,
+): string | null {
+  const color = yc(theme, colors?.[colorKey]);
+  if (color == null) return null;
+
+  return variablesToCSS(
+    `.x-theme-toast--${colorKey}`,
+    toastColorVariables(color),
+  );
+}
+
+function templateTagCSS(
+  theme: Theme,
+  colorKey: YaakColorKey,
+  colors?: ThemeComponentColors,
+): string | null {
+  const color = yc(theme, colors?.[colorKey]);
+  if (color == null) return null;
+
+  return variablesToCSS(
+    `.x-theme-templateTag--${colorKey}`,
+    templateTagColorVariables(color),
+  );
+}
+
+export function getThemeCSS(theme: Theme): string {
+  theme.components = theme.components ?? {};
+  theme.components.toast =
+    theme.components.toast ?? theme.components.menu ?? {};
+  const { components, id, label } = theme;
+  const colors = Object.keys(theme.base).reduce((prev, key) => {
+    return { ...prev, [key]: theme.base[key as YaakColorKey] };
+  }, {} as ThemeComponentColors);
+
+  let themeCSS = "";
+  try {
+    const baseCss = variablesToCSS(null, themeVariables(theme));
+    themeCSS = [
+      baseCss,
+      ...Object.keys(components).map((key) =>
+        componentCSS(theme, key as ComponentName),
+      ),
+      variablesToCSS(
+        ".x-theme-button--solid--default",
+        buttonSolidColorVariables(yc(theme, theme.base.surface), true),
+      ),
+      variablesToCSS(
+        ".x-theme-button--border--default",
+        buttonBorderColorVariables(yc(theme, theme.base.surface), true),
+      ),
+      ...Object.keys(colors).map((key) =>
+        buttonCSS(
+          theme,
+          key as YaakColorKey,
+          theme.components?.button ?? colors,
+        ),
+      ),
+      ...Object.keys(colors).map((key) =>
+        bannerCSS(
+          theme,
+          key as YaakColorKey,
+          theme.components?.banner ?? colors,
+        ),
+      ),
+      ...Object.keys(colors).map((key) =>
+        toastCSS(
+          theme,
+          key as YaakColorKey,
+          theme.components?.banner ?? colors,
+        ),
+      ),
+      ...Object.keys(colors).map((key) =>
+        templateTagCSS(
+          theme,
+          key as YaakColorKey,
+          theme.components?.templateTag ?? colors,
+        ),
+      ),
+    ].join("\n\n");
+  } catch (err) {
+    console.error("Failed to generate CSS", err);
+  }
+
+  return [
+    `/* ${label} */`,
+    `[data-theme="${id}"] {`,
+    indent(themeCSS),
+    "}",
+  ].join("\n");
+}
+
+export function addThemeStylesToDocument(rawTheme: Theme | null) {
+  if (rawTheme == null) {
+    console.error("Failed to add theme styles: theme is null");
+    return;
+  }
+
+  const theme = completeTheme(rawTheme);
+  let styleEl = document.head.querySelector("style[data-theme]");
+  if (!styleEl) {
+    styleEl = document.createElement("style");
+    document.head.appendChild(styleEl);
+  }
+
+  styleEl.setAttribute("data-theme", theme.id);
+  styleEl.setAttribute("data-updated-at", new Date().toISOString());
+  styleEl.textContent = getThemeCSS(theme);
+}
+
+export function setThemeOnDocument(theme: Theme | null) {
+  if (theme == null) {
+    console.error("Failed to set theme: theme is null");
+    return;
+  }
+
+  document.documentElement.setAttribute("data-theme", theme.id);
+}
+
+export function applyThemeToDocument(theme: Theme | null) {
+  addThemeStylesToDocument(theme);
+  setThemeOnDocument(theme);
+}
+
+export function platformFromUserAgent(userAgent: string): DocumentPlatform {
+  const normalized = userAgent.toLowerCase();
+
+  if (normalized.includes("linux")) return "linux";
+  if (normalized.includes("mac os") || normalized.includes("macintosh"))
+    return "macos";
+  if (normalized.includes("win")) return "windows";
+  return "unknown";
+}
+
+export function setPlatformOnDocument(platform: string | null | undefined) {
+  const normalized =
+    platform === "linux" || platform === "macos" || platform === "windows"
+      ? platform
+      : "unknown";
+  document.documentElement.setAttribute("data-platform", normalized);
+}
+
+export function indent(text: string, space = "    "): string {
+  return text
+    .split("\n")
+    .map((line) => space + line)
+    .join("\n");
+}
+
+function yc<T extends string | null | undefined>(
+  theme: Theme,
+  value: T,
+): T extends string ? YaakColor : null {
+  if (value == null) return null as never;
+  return new YaakColor(value, theme.dark ? "dark" : "light") as never;
+}
+
+export function completeTheme(theme: Theme): Theme {
+  const fallback = theme.dark ? defaultDarkTheme.base : defaultLightTheme.base;
+  const color = (value: string | null | undefined) => yc(theme, value);
+
+  theme.base.primary ??= fallback.primary;
+  theme.base.secondary ??= fallback.secondary;
+  theme.base.info ??= fallback.info;
+  theme.base.success ??= fallback.success;
+  theme.base.notice ??= fallback.notice;
+  theme.base.warning ??= fallback.warning;
+  theme.base.danger ??= fallback.danger;
+
+  theme.base.surface ??= fallback.surface;
+  theme.base.surfaceHighlight ??= color(theme.base.surface)?.lift(0.06)?.css();
+  theme.base.surfaceActive ??= color(theme.base.primary)
+    ?.lower(0.2)
+    .translucify(0.8)
+    .css();
+
+  theme.base.border ??= color(theme.base.surface)?.lift(0.12)?.css();
+  theme.base.borderSubtle ??= color(theme.base.border)?.lower(0.08)?.css();
+
+  theme.base.text ??= fallback.text;
+  theme.base.textSubtle ??= color(theme.base.text)?.lower(0.3)?.css();
+  theme.base.textSubtlest ??= color(theme.base.text)?.lower(0.5)?.css();
+
+  return theme;
+}
diff --git a/packages/theme/src/yaakColor.ts b/packages/theme/src/yaakColor.ts
new file mode 100644
index 00000000..5b3731b4
--- /dev/null
+++ b/packages/theme/src/yaakColor.ts
@@ -0,0 +1,153 @@
+import parseColor from "parse-color";
+
+export class YaakColor {
+  private readonly appearance: "dark" | "light" = "light";
+
+  private hue = 0;
+  private saturation = 0;
+  private lightness = 0;
+  private alpha = 1;
+
+  constructor(cssColor: string, appearance: "dark" | "light" = "light") {
+    try {
+      this.set(cssColor);
+      this.appearance = appearance;
+    } catch (err) {
+      console.log("Failed to parse CSS color", cssColor, err);
+    }
+  }
+
+  static transparent(): YaakColor {
+    return new YaakColor("rgb(0,0,0)", "light").translucify(1);
+  }
+
+  static white(): YaakColor {
+    return new YaakColor("rgb(0,0,0)", "light").lower(1);
+  }
+
+  static black(): YaakColor {
+    return new YaakColor("rgb(0,0,0)", "light").lift(1);
+  }
+
+  set(cssColor: string): YaakColor {
+    let fixedCssColor = cssColor;
+    if (cssColor.startsWith("#") && cssColor.length === 9) {
+      const [r, g, b, a] = hexToRgba(cssColor);
+      fixedCssColor = `rgba(${r},${g},${b},${a})`;
+    }
+    const { hsla } = parseColor(fixedCssColor);
+    this.hue = hsla[0];
+    this.saturation = hsla[1];
+    this.lightness = hsla[2];
+    this.alpha = hsla[3] ?? 1;
+    return this;
+  }
+
+  clone(): YaakColor {
+    return new YaakColor(this.css(), this.appearance);
+  }
+
+  lower(mod: number): YaakColor {
+    return this.appearance === "dark" ? this._darken(mod) : this._lighten(mod);
+  }
+
+  lift(mod: number): YaakColor {
+    return this.appearance === "dark" ? this._lighten(mod) : this._darken(mod);
+  }
+
+  minLightness(n: number): YaakColor {
+    const color = this.clone();
+    if (color.lightness < n) {
+      color.lightness = n;
+    }
+    return color;
+  }
+
+  isDark(): boolean {
+    return this.lightness < 50;
+  }
+
+  translucify(mod: number): YaakColor {
+    const color = this.clone();
+    color.alpha = color.alpha - color.alpha * mod;
+    return color;
+  }
+
+  opacify(mod: number): YaakColor {
+    const color = this.clone();
+    color.alpha = this.alpha + (100 - this.alpha) * mod;
+    return color;
+  }
+
+  desaturate(mod: number): YaakColor {
+    const color = this.clone();
+    color.saturation = color.saturation - color.saturation * mod;
+    return color;
+  }
+
+  saturate(mod: number): YaakColor {
+    const color = this.clone();
+    color.saturation = this.saturation + (100 - this.saturation) * mod;
+    return color;
+  }
+
+  lighterThan(color: YaakColor): boolean {
+    return this.lightness > color.lightness;
+  }
+
+  css(): string {
+    const [r, g, b] = parseColor(
+      `hsl(${this.hue},${this.saturation}%,${this.lightness}%)`,
+    ).rgb;
+    return rgbaToHex(r, g, b, this.alpha);
+  }
+
+  hexNoAlpha(): string {
+    const [r, g, b] = parseColor(
+      `hsl(${this.hue},${this.saturation}%,${this.lightness}%)`,
+    ).rgb;
+    return rgbaToHexNoAlpha(r, g, b);
+  }
+
+  private _lighten(mod: number): YaakColor {
+    const color = this.clone();
+    color.lightness = this.lightness + (100 - this.lightness) * mod;
+    return color;
+  }
+
+  private _darken(mod: number): YaakColor {
+    const color = this.clone();
+    color.lightness = this.lightness - this.lightness * mod;
+    return color;
+  }
+}
+
+function rgbaToHex(r: number, g: number, b: number, a: number): string {
+  const toHex = (n: number): string => {
+    const hex = Number(Math.round(n)).toString(16);
+    return hex.length === 1 ? `0${hex}` : hex;
+  };
+  return `#${[toHex(r), toHex(g), toHex(b), toHex(a * 255)].join("").toUpperCase()}`;
+}
+
+function rgbaToHexNoAlpha(r: number, g: number, b: number): string {
+  const toHex = (n: number): string => {
+    const hex = Number(Math.round(n)).toString(16);
+    return hex.length === 1 ? `0${hex}` : hex;
+  };
+  return `#${[toHex(r), toHex(g), toHex(b)].join("").toUpperCase()}`;
+}
+
+function hexToRgba(hex: string): [number, number, number, number] {
+  const fromHex = (value: string): number => {
+    if (value === "") return 255;
+    return Number(`0x${value}`);
+  };
+
+  const r = fromHex(hex.slice(1, 3));
+  const g = fromHex(hex.slice(3, 5));
+  const b = fromHex(hex.slice(5, 7));
+  const a = fromHex(hex.slice(7, 9));
+
+  return [r, g, b, a / 255];
+}
diff --git a/packages/theme/tsconfig.json b/packages/theme/tsconfig.json
new file mode 100644
index 00000000..77592bbb
--- /dev/null
+++ b/packages/theme/tsconfig.json
@@ -0,0 +1,12 @@
+{
+  "compilerOptions": {
+    "target": "es2021",
+    "lib": ["DOM", "DOM.Iterable", "ESNext"],
+    "strict": true,
+    "module": "ESNext",
+    "moduleResolution": "Node",
+    "jsx": "react-jsx",
+    "noEmit": true
+  },
+  "include": ["src"]
+}
diff --git a/packages/ui/package.json b/packages/ui/package.json
new file mode 100644
index 00000000..b97529d0
--- /dev/null
+++ b/packages/ui/package.json
@@ -0,0 +1,16 @@
+{
+  "name": "@yaakapp-internal/ui",
+  "private": true,
+  "version": "1.0.0",
+  "type": "module",
+  "main": "src/index.ts",
+  "types": "src/index.ts",
+  "dependencies": {
+    "react": "^19.1.0",
+    "react-dom": "^19.1.0"
+  },
+  "peerDependencies": {
+    "react": "^19.1.0",
+    "react-dom": "^19.1.0"
+  }
+}
diff --git a/packages/ui/src/components/Button.tsx b/packages/ui/src/components/Button.tsx
new file mode 100644
index 00000000..05a36d2f
--- /dev/null
+++ b/packages/ui/src/components/Button.tsx
@@ -0,0 +1,123 @@
+import type { HTMLAttributes, ReactNode } from "react";
+
+type ButtonColor =
+  | "default"
+  | "custom"
+  | "primary"
+  | "secondary"
+  | "info"
+  | "success"
+  | "notice"
+  | "warning"
+  | "danger";
+
+type ButtonVariant = "border" | "solid";
+type ButtonSize = "2xs" | "xs" | "sm" | "md" | "auto";
+
+export type ButtonProps = Omit<
+  HTMLAttributes<HTMLButtonElement>,
+  "color" | "onChange"
+> & {
+  innerClassName?: string;
+  color?: ButtonColor;
+  tone?: Exclude<ButtonColor, "custom">;
+  variant?: ButtonVariant;
+  isLoading?: boolean;
+  size?: ButtonSize;
+  justify?: "start" | "center";
+  type?: "button" | "submit";
+  disabled?: boolean;
+  title?: string;
+  leftSlot?: ReactNode;
+  rightSlot?: ReactNode;
+};
+
+function cx(...values: Array<string | false | null | undefined>) {
+  return values.filter(Boolean).join(" ");
+}
+
+export function Button({
+  isLoading,
+  className,
+  innerClassName,
+  children,
+  color,
+  tone,
+  type = "button",
+  justify = "center",
+  size = "md",
+  variant = "solid",
+  leftSlot,
+  rightSlot,
+  disabled,
+  title,
+  onClick,
+  ...props
+}: ButtonProps) {
+  const resolvedColor = color ?? tone ?? "default";
+  const isDisabled = disabled || isLoading;
+
+  return (
+    <button
+      type={type}
+      className={cx(
+        className,
+        "x-theme-button",
+        `x-theme-button--${variant}`,
+        `x-theme-button--${variant}--${resolvedColor}`,
+        "border",
+        "max-w-full min-w-0",
+        "hocus:opacity-100",
+        "whitespace-nowrap outline-none",
+        "flex-shrink-0 flex items-center",
+        "outline-0",
+        isDisabled ? "pointer-events-none opacity-disabled" : "pointer-events-auto",
+        justify === "start" && "justify-start",
+        justify === "center" && "justify-center",
+        size === "md" && "h-md px-3 rounded-md",
+        size === "sm" && "h-sm px-2.5 rounded-md",
+        size === "xs" && "h-xs px-2 text-sm rounded-md",
+        size === "2xs" && "h-2xs px-2 text-xs rounded",
+        size === "auto" && "px-3 py-2 rounded-md",
+        variant === "solid" && "border-transparent",
+        variant === "solid" &&
+          resolvedColor === "custom" &&
+          "focus-visible:outline-2 outline-border-focus",
+        variant === "solid" &&
+          resolvedColor !== "custom" &&
+          "text-text enabled:hocus:text-text enabled:hocus:bg-surface-highlight outline-border-subtle",
+        variant === "solid" &&
+          resolvedColor !== "custom" &&
+          resolvedColor !== "default" &&
+          "bg-surface",
+        variant === "border" && "border",
+        variant === "border" &&
+          resolvedColor !== "custom" &&
+          "border-border-subtle text-text-subtle enabled:hocus:border-border enabled:hocus:bg-surface-highlight enabled:hocus:text-text outline-border-subtler",
+      )}
+      disabled={isDisabled}
+      onClick={onClick}
+      onDoubleClick={(e) => {
+        e.stopPropagation();
+      }}
+      title={title}
+      {...props}
+    >
+      {isLoading ? (
+        <div className="mr-1">...</div>
+      ) : leftSlot ? (
+        <div className="mr-2">{leftSlot}</div>
+      ) : null}
+      <div
+        className={cx(
+          "truncate w-full",
+          justify === "start" ? "text-left" : "text-center",
+          innerClassName,
+        )}
+      >
+        {children}
+      </div>
+      {rightSlot ? <div className="ml-1">{rightSlot}</div> : null}
+    </button>
+  );
+}
diff --git a/packages/ui/src/index.ts b/packages/ui/src/index.ts
new file mode 100644
index 00000000..5925536a
--- /dev/null
+++ b/packages/ui/src/index.ts
@@ -0,0 +1,2 @@
+export { Button } from "./components/Button";
+export type { ButtonProps } from "./components/Button";
diff --git a/packages/ui/tsconfig.json b/packages/ui/tsconfig.json
new file mode 100644
index 00000000..77592bbb
--- /dev/null
+++ b/packages/ui/tsconfig.json
@@ -0,0 +1,12 @@
+{
+  "compilerOptions": {
+    "target": "es2021",
+    "lib": ["DOM", "DOM.Iterable", "ESNext"],
+    "strict": true,
+    "module": "ESNext",
+    "moduleResolution": "Node",
+    "jsx": "react-jsx",
+    "noEmit": true
+  },
+  "include": ["src"]
+}