diff --git a/packages/backend/src/server/web/boot.js b/packages/backend/src/server/web/boot.js
index 5e52360456..c28fa88f5c 100644
--- a/packages/backend/src/server/web/boot.js
+++ b/packages/backend/src/server/web/boot.js
@@ -3,17 +3,6 @@
  * SPDX-License-Identifier: AGPL-3.0-only
  */
 
-/**
- * BOOT LOADER
- * サーバーからレスポンスされるHTMLに埋め込まれるスクリプトで、以下の役割を持ちます。
- * - 翻訳ファイルをフェッチする。
- * - バージョンに基づいて適切なメインスクリプトを読み込む。
- * - キャッシュされたコンパイル済みテーマを適用する。
- * - クライアントの設定値に基づいて対応するHTMLクラス等を設定する。
- * テーマをこの段階で設定するのは、メインスクリプトが読み込まれる間もテーマを適用したいためです。
- * 注: webpackは介さないため、このファイルではrequireやimportは使えません。
- */
-
 'use strict';
 
 // ブロックの中に入れないと、定義した変数がブラウザのグローバルスコープに登録されてしまい邪魔なので
@@ -320,6 +309,6 @@
 			#errorInfo {
 				width: 50%;
 			}
-		}`)
+		}`);
 	}
 })();
diff --git a/packages/frontend-embed/src/theme.ts b/packages/frontend-embed/src/theme.ts
new file mode 100644
index 0000000000..050d8cf63b
--- /dev/null
+++ b/packages/frontend-embed/src/theme.ts
@@ -0,0 +1,102 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and misskey-project
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import tinycolor from 'tinycolor2';
+import lightTheme from '@@/themes/_light.json5';
+import darkTheme from '@@/themes/_dark.json5';
+import type { BundledTheme } from 'shiki/themes';
+
+export type Theme = {
+	id: string;
+	name: string;
+	author: string;
+	desc?: string;
+	base?: 'dark' | 'light';
+	props: Record<string, string>;
+	codeHighlighter?: {
+		base: BundledTheme;
+		overrides?: Record<string, any>;
+	} | {
+		base: '_none_';
+		overrides: Record<string, any>;
+	};
+};
+
+let timeout: number | null = null;
+
+export function applyTheme(theme: Theme, persist = true) {
+	if (timeout) window.clearTimeout(timeout);
+
+	document.documentElement.classList.add('_themeChanging_');
+
+	timeout = window.setTimeout(() => {
+		document.documentElement.classList.remove('_themeChanging_');
+	}, 1000);
+
+	const colorScheme = theme.base === 'dark' ? 'dark' : 'light';
+
+	// Deep copy
+	const _theme = JSON.parse(JSON.stringify(theme));
+
+	if (_theme.base) {
+		const base = [lightTheme, darkTheme].find(x => x.id === _theme.base);
+		if (base) _theme.props = Object.assign({}, base.props, _theme.props);
+	}
+
+	const props = compile(_theme);
+
+	for (const tag of document.head.children) {
+		if (tag.tagName === 'META' && tag.getAttribute('name') === 'theme-color') {
+			tag.setAttribute('content', props['htmlThemeColor']);
+			break;
+		}
+	}
+
+	for (const [k, v] of Object.entries(props)) {
+		document.documentElement.style.setProperty(`--${k}`, v.toString());
+	}
+
+	document.documentElement.style.setProperty('color-scheme', colorScheme);
+}
+
+function compile(theme: Theme): Record<string, string> {
+	function getColor(val: string): tinycolor.Instance {
+		if (val[0] === '@') { // ref (prop)
+			return getColor(theme.props[val.substring(1)]);
+		} else if (val[0] === '$') { // ref (const)
+			return getColor(theme.props[val]);
+		} else if (val[0] === ':') { // func
+			const parts = val.split('<');
+			const func = parts.shift().substring(1);
+			const arg = parseFloat(parts.shift());
+			const color = getColor(parts.join('<'));
+
+			switch (func) {
+				case 'darken': return color.darken(arg);
+				case 'lighten': return color.lighten(arg);
+				case 'alpha': return color.setAlpha(arg);
+				case 'hue': return color.spin(arg);
+				case 'saturate': return color.saturate(arg);
+			}
+		}
+
+		// other case
+		return tinycolor(val);
+	}
+
+	const props = {};
+
+	for (const [k, v] of Object.entries(theme.props)) {
+		if (k.startsWith('$')) continue; // ignore const
+
+		props[k] = v.startsWith('"') ? v.replace(/^"\s*/, '') : genValue(getColor(v));
+	}
+
+	return props;
+}
+
+function genValue(c: tinycolor.Instance): string {
+	return c.toRgbString();
+}
diff --git a/packages/frontend-embed/tsconfig.json b/packages/frontend-embed/tsconfig.json
index fe4d202894..b88773b598 100644
--- a/packages/frontend-embed/tsconfig.json
+++ b/packages/frontend-embed/tsconfig.json
@@ -23,7 +23,8 @@
 		"useDefineForClassFields": true,
 		"baseUrl": ".",
 		"paths": {
-			"@/*": ["./src/*"]
+			"@/*": ["./src/*"],
+			"@@/*": ["../frontend-shared/*"]
 		},
 		"typeRoots": [
 			"./@types",
diff --git a/packages/frontend-embed/vite.config.ts b/packages/frontend-embed/vite.config.ts
index 9715751ae8..72c9690dd8 100644
--- a/packages/frontend-embed/vite.config.ts
+++ b/packages/frontend-embed/vite.config.ts
@@ -72,6 +72,7 @@ export function getConfig(): UserConfig {
 			extensions,
 			alias: {
 				'@/': __dirname + '/src/',
+				'@@/': __dirname + '/../frontend-shared/',
 				'/client-assets/': __dirname + '/assets/',
 				'/static-assets/': __dirname + '/../backend/assets/'
 			},
diff --git a/packages/frontend/src/themes/_dark.json5 b/packages/frontend-shared/themes/_dark.json5
similarity index 100%
rename from packages/frontend/src/themes/_dark.json5
rename to packages/frontend-shared/themes/_dark.json5
diff --git a/packages/frontend/src/themes/_light.json5 b/packages/frontend-shared/themes/_light.json5
similarity index 100%
rename from packages/frontend/src/themes/_light.json5
rename to packages/frontend-shared/themes/_light.json5
diff --git a/packages/frontend/src/themes/d-astro.json5 b/packages/frontend-shared/themes/d-astro.json5
similarity index 100%
rename from packages/frontend/src/themes/d-astro.json5
rename to packages/frontend-shared/themes/d-astro.json5
diff --git a/packages/frontend/src/themes/d-botanical.json5 b/packages/frontend-shared/themes/d-botanical.json5
similarity index 100%
rename from packages/frontend/src/themes/d-botanical.json5
rename to packages/frontend-shared/themes/d-botanical.json5
diff --git a/packages/frontend/src/themes/d-cherry.json5 b/packages/frontend-shared/themes/d-cherry.json5
similarity index 100%
rename from packages/frontend/src/themes/d-cherry.json5
rename to packages/frontend-shared/themes/d-cherry.json5
diff --git a/packages/frontend/src/themes/d-dark.json5 b/packages/frontend-shared/themes/d-dark.json5
similarity index 100%
rename from packages/frontend/src/themes/d-dark.json5
rename to packages/frontend-shared/themes/d-dark.json5
diff --git a/packages/frontend/src/themes/d-future.json5 b/packages/frontend-shared/themes/d-future.json5
similarity index 100%
rename from packages/frontend/src/themes/d-future.json5
rename to packages/frontend-shared/themes/d-future.json5
diff --git a/packages/frontend/src/themes/d-green-lime.json5 b/packages/frontend-shared/themes/d-green-lime.json5
similarity index 100%
rename from packages/frontend/src/themes/d-green-lime.json5
rename to packages/frontend-shared/themes/d-green-lime.json5
diff --git a/packages/frontend/src/themes/d-green-orange.json5 b/packages/frontend-shared/themes/d-green-orange.json5
similarity index 100%
rename from packages/frontend/src/themes/d-green-orange.json5
rename to packages/frontend-shared/themes/d-green-orange.json5
diff --git a/packages/frontend/src/themes/d-ice.json5 b/packages/frontend-shared/themes/d-ice.json5
similarity index 100%
rename from packages/frontend/src/themes/d-ice.json5
rename to packages/frontend-shared/themes/d-ice.json5
diff --git a/packages/frontend/src/themes/d-persimmon.json5 b/packages/frontend-shared/themes/d-persimmon.json5
similarity index 100%
rename from packages/frontend/src/themes/d-persimmon.json5
rename to packages/frontend-shared/themes/d-persimmon.json5
diff --git a/packages/frontend/src/themes/d-u0.json5 b/packages/frontend-shared/themes/d-u0.json5
similarity index 100%
rename from packages/frontend/src/themes/d-u0.json5
rename to packages/frontend-shared/themes/d-u0.json5
diff --git a/packages/frontend/src/themes/l-apricot.json5 b/packages/frontend-shared/themes/l-apricot.json5
similarity index 100%
rename from packages/frontend/src/themes/l-apricot.json5
rename to packages/frontend-shared/themes/l-apricot.json5
diff --git a/packages/frontend/src/themes/l-botanical.json5 b/packages/frontend-shared/themes/l-botanical.json5
similarity index 100%
rename from packages/frontend/src/themes/l-botanical.json5
rename to packages/frontend-shared/themes/l-botanical.json5
diff --git a/packages/frontend/src/themes/l-cherry.json5 b/packages/frontend-shared/themes/l-cherry.json5
similarity index 100%
rename from packages/frontend/src/themes/l-cherry.json5
rename to packages/frontend-shared/themes/l-cherry.json5
diff --git a/packages/frontend/src/themes/l-coffee.json5 b/packages/frontend-shared/themes/l-coffee.json5
similarity index 100%
rename from packages/frontend/src/themes/l-coffee.json5
rename to packages/frontend-shared/themes/l-coffee.json5
diff --git a/packages/frontend/src/themes/l-light.json5 b/packages/frontend-shared/themes/l-light.json5
similarity index 100%
rename from packages/frontend/src/themes/l-light.json5
rename to packages/frontend-shared/themes/l-light.json5
diff --git a/packages/frontend/src/themes/l-rainy.json5 b/packages/frontend-shared/themes/l-rainy.json5
similarity index 100%
rename from packages/frontend/src/themes/l-rainy.json5
rename to packages/frontend-shared/themes/l-rainy.json5
diff --git a/packages/frontend/src/themes/l-sushi.json5 b/packages/frontend-shared/themes/l-sushi.json5
similarity index 100%
rename from packages/frontend/src/themes/l-sushi.json5
rename to packages/frontend-shared/themes/l-sushi.json5
diff --git a/packages/frontend/src/themes/l-u0.json5 b/packages/frontend-shared/themes/l-u0.json5
similarity index 100%
rename from packages/frontend/src/themes/l-u0.json5
rename to packages/frontend-shared/themes/l-u0.json5
diff --git a/packages/frontend/src/themes/l-vivid.json5 b/packages/frontend-shared/themes/l-vivid.json5
similarity index 100%
rename from packages/frontend/src/themes/l-vivid.json5
rename to packages/frontend-shared/themes/l-vivid.json5
diff --git a/packages/frontend/src/pages/theme-editor.vue b/packages/frontend/src/pages/theme-editor.vue
index 50c3beeabc..fe7896b7d9 100644
--- a/packages/frontend/src/pages/theme-editor.vue
+++ b/packages/frontend/src/pages/theme-editor.vue
@@ -79,6 +79,8 @@ import tinycolor from 'tinycolor2';
 import { v4 as uuid } from 'uuid';
 import JSON5 from 'json5';
 
+import lightTheme from '@@/themes/_light.json5';
+import darkTheme from '@@/themes/_dark.json5';
 import MkButton from '@/components/MkButton.vue';
 import MkCodeEditor from '@/components/MkCodeEditor.vue';
 import MkTextarea from '@/components/MkTextarea.vue';
@@ -86,8 +88,6 @@ import MkFolder from '@/components/MkFolder.vue';
 
 import { $i } from '@/account.js';
 import { Theme, applyTheme } from '@/scripts/theme.js';
-import lightTheme from '@/themes/_light.json5';
-import darkTheme from '@/themes/_dark.json5';
 import { host } from '@/config.js';
 import * as os from '@/os.js';
 import { ColdDeviceStorage, defaultStore } from '@/store.js';
diff --git a/packages/frontend/src/scripts/code-highlighter.ts b/packages/frontend/src/scripts/code-highlighter.ts
index e94027d302..b0ffac93d7 100644
--- a/packages/frontend/src/scripts/code-highlighter.ts
+++ b/packages/frontend/src/scripts/code-highlighter.ts
@@ -7,13 +7,13 @@ import { getHighlighterCore, loadWasm } from 'shiki/core';
 import darkPlus from 'shiki/themes/dark-plus.mjs';
 import { bundledThemesInfo } from 'shiki/themes';
 import { bundledLanguagesInfo } from 'shiki/langs';
+import lightTheme from '@@/themes/_light.json5';
+import darkTheme from '@@/themes/_dark.json5';
 import { unique } from './array.js';
 import { deepClone } from './clone.js';
 import { deepMerge } from './merge.js';
 import type { HighlighterCore, LanguageRegistration, ThemeRegistration, ThemeRegistrationRaw } from 'shiki/core';
 import { ColdDeviceStorage } from '@/store.js';
-import lightTheme from '@/themes/_light.json5';
-import darkTheme from '@/themes/_dark.json5';
 
 let _highlighter: HighlighterCore | null = null;
 
diff --git a/packages/frontend/src/scripts/theme.ts b/packages/frontend/src/scripts/theme.ts
index c7f8b3d596..9b9f1f030c 100644
--- a/packages/frontend/src/scripts/theme.ts
+++ b/packages/frontend/src/scripts/theme.ts
@@ -5,11 +5,11 @@
 
 import { ref } from 'vue';
 import tinycolor from 'tinycolor2';
+import lightTheme from '@@/themes/_light.json5';
+import darkTheme from '@@/themes/_dark.json5';
 import { deepClone } from './clone.js';
 import type { BundledTheme } from 'shiki/themes';
 import { globalEvents } from '@/events.js';
-import lightTheme from '@/themes/_light.json5';
-import darkTheme from '@/themes/_dark.json5';
 import { miLocalStorage } from '@/local-storage.js';
 
 export type Theme = {
diff --git a/packages/frontend/src/store.ts b/packages/frontend/src/store.ts
index 437314074a..0bf499bb4d 100644
--- a/packages/frontend/src/store.ts
+++ b/packages/frontend/src/store.ts
@@ -458,10 +458,10 @@ export const defaultStore = markRaw(new Storage('base', {
 		where: 'device',
 		default: false,
 	},
-  contextMenu: {
+	contextMenu: {
 		where: 'device',
 		default: 'app' as 'app' | 'appWithShift' | 'native',
-  },
+	},
 
 	sound_masterVolume: {
 		where: 'device',
@@ -520,8 +520,8 @@ interface Watcher {
 /**
  * 常にメモリにロードしておく必要がないような設定情報を保管するストレージ(非リアクティブ)
  */
-import lightTheme from '@/themes/l-light.json5';
-import darkTheme from '@/themes/d-green-lime.json5';
+import lightTheme from '@@/themes/l-light.json5';
+import darkTheme from '@@/themes/d-green-lime.json5';
 
 export class ColdDeviceStorage {
 	public static default = {
@@ -558,7 +558,7 @@ export class ColdDeviceStorage {
 	public static set<T extends keyof typeof ColdDeviceStorage.default>(key: T, value: typeof ColdDeviceStorage.default[T]): void {
 		// 呼び出し側のバグ等で undefined が来ることがある
 		// undefined を文字列として miLocalStorage に入れると参照する際の JSON.parse でコケて不具合の元になるため無視
-		// eslint-disable-next-line @typescript-eslint/no-unnecessary-condition
+		 
 		if (value === undefined) {
 			console.error(`attempt to store undefined value for key '${key}'`);
 			return;
diff --git a/packages/frontend/tsconfig.json b/packages/frontend/tsconfig.json
index fe4d202894..b88773b598 100644
--- a/packages/frontend/tsconfig.json
+++ b/packages/frontend/tsconfig.json
@@ -23,7 +23,8 @@
 		"useDefineForClassFields": true,
 		"baseUrl": ".",
 		"paths": {
-			"@/*": ["./src/*"]
+			"@/*": ["./src/*"],
+			"@@/*": ["../frontend-shared/*"]
 		},
 		"typeRoots": [
 			"./@types",
diff --git a/packages/frontend/vite.config.ts b/packages/frontend/vite.config.ts
index d7a5b13d26..bb3fe7f4a7 100644
--- a/packages/frontend/vite.config.ts
+++ b/packages/frontend/vite.config.ts
@@ -87,6 +87,7 @@ export function getConfig(): UserConfig {
 			extensions,
 			alias: {
 				'@/': __dirname + '/src/',
+				'@@/': __dirname + '/../frontend-shared/',
 				'/client-assets/': __dirname + '/assets/',
 				'/static-assets/': __dirname + '/../backend/assets/',
 				'/fluent-emojis/': __dirname + '/../../fluent-emojis/dist/',