Centralize darkThemes list, fix dark themes reverting to light on restart

src/lib/platform.ts

@@ -5,3 +5,37 @@ const ua = typeof navigator !== 'undefined' ? navigator.userAgent : '';
 export const isAndroid = /android/i.test(ua);
 export const isIOS = /iphone|ipad|ipod/i.test(ua);
 export const isMobile = isAndroid || isIOS;
+
+// Themes that use the dark color scheme. Used by applyTheme() to toggle the
+// `dark` class on the root element. Keep this in sync when adding new themes.
+export const darkThemes = [
+	'dark',
+	'solarized-dark',
+	'catppuccin',
+	'nord',
+	'tokyo-night',
+	'github-dark',
+	'dracula',
+	'blueberry',
+	'forest-green',
+	'gruvbox',
+	'midnight-tide',
+	'cherry-blossom',
+	'synthwave',
+	'ember',
+	'moonlit',
+	'dark-coffee',
+	'crimson',
+	'material-dark',
+	'monokai',
+	'rose-pine',
+	'everforest',
+	'horizon',
+	'cyberpunk',
+	'black',
+	'one-dark',
+];
+
+export function isDarkTheme(theme: string): boolean {
+	return darkThemes.includes(theme) || (theme === 'system' && typeof window !== 'undefined' && window.matchMedia('(prefers-color-scheme: dark)').matches);
+}