2025-09-29 16:33:15 +08:00
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/**
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* Checks for common dark mode CSS classes on the html or body elements.
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* @returns {boolean} - True if a common dark mode class is found.
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*/
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function hasDarkModeClass() {
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2025-12-17 14:18:28 +08:00
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const DEFAULT_DARK_MODE_CLASSES = ['dark', 'dark-mode', 'theme-dark', 'night', 'night-mode']
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2025-09-29 16:33:15 +08:00
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const htmlElement = document.documentElement
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2025-12-17 14:40:11 +08:00
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const bodyElement = document.body || document.documentElement // can be null in some cases
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2025-09-29 16:33:15 +08:00
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// Check class names on <html> and <body>
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2025-12-17 14:18:28 +08:00
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for (const className of DEFAULT_DARK_MODE_CLASSES) {
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2025-12-17 14:40:11 +08:00
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if (htmlElement.classList.contains(className) || bodyElement?.classList.contains(className)) {
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2025-09-29 16:33:15 +08:00
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return true
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}
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}
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2026-04-20 20:14:07 -04:00
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// Some sites use data attributes (data-theme, data-color-mode, data-bs-theme, etc.)
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const dataAttrs = ['data-theme', 'data-color-mode', 'data-bs-theme', 'data-color-scheme']
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for (const attr of dataAttrs) {
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2026-03-30 18:16:15 -04:00
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const bodyValue = bodyElement?.getAttribute(attr)
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const htmlValue = htmlElement.getAttribute(attr)
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if (bodyValue?.toLowerCase().includes('dark') || htmlValue?.toLowerCase().includes('dark')) {
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2026-04-20 20:14:07 -04:00
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return true
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}
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2025-09-29 16:33:15 +08:00
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}
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return false
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}
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/**
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* Parses an RGB or RGBA color string and returns an object with r, g, b properties.
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* @param {string} colorString - e.g., "rgb(34, 34, 34)" or "rgba(0, 0, 0, 0.5)"
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* @returns {{r: number, g: number, b: number}|null}
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*/
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function parseRgbColor(colorString: string) {
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const rgbMatch = /rgba?\((\d+),\s*(\d+),\s*(\d+)/.exec(colorString)
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if (!rgbMatch) {
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return null // Not a valid rgb/rgba string
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}
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return {
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r: parseInt(rgbMatch[1]),
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g: parseInt(rgbMatch[2]),
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b: parseInt(rgbMatch[3]),
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}
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}
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/**
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* Determines if a color is "dark" based on its calculated luminance.
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* @param {string} colorString - The CSS color string (e.g., "rgb(50, 50, 50)").
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* @param {number} threshold - A value between 0 and 255. Colors with luminance below this will be considered dark. Default is 128.
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* @returns {boolean} - True if the color is considered dark.
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*/
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function isColorDark(colorString: string, threshold = 128) {
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if (!colorString || colorString === 'transparent' || colorString.startsWith('rgba(0, 0, 0, 0)')) {
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return false // Transparent is not dark
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}
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const rgb = parseRgbColor(colorString)
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if (!rgb) {
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return false // Could not parse color
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}
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// Calculate perceived luminance using the standard formula
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const luminance = 0.299 * rgb.r + 0.587 * rgb.g + 0.114 * rgb.b
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return luminance < threshold
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}
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/**
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* Checks the background color of the body element to determine if the page is dark.
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* @returns {boolean}
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*/
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function isBackgroundDark() {
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// We check both <html> and <body> because some pages set the color on <html>
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const htmlStyle = window.getComputedStyle(document.documentElement)
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2025-12-17 14:40:11 +08:00
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const bodyStyle = window.getComputedStyle(document.body || document.documentElement)
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2025-09-29 16:33:15 +08:00
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// Get background colors
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const htmlBgColor = htmlStyle.backgroundColor
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const bodyBgColor = bodyStyle.backgroundColor
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// The body's background might be transparent, in which case we should
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// fall back to the html element's background.
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if (isColorDark(bodyBgColor)) {
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return true
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} else if (bodyBgColor === 'transparent' || bodyBgColor.startsWith('rgba(0, 0, 0, 0)')) {
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return isColorDark(htmlBgColor)
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}
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return false
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}
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2026-04-20 20:14:07 -04:00
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/**
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* Checks the CSS `color-scheme` property and `<meta name="color-scheme">` tag.
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* @returns {boolean | null} - True/false if deterministic, null if inconclusive.
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*/
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function getColorSchemePreference(): boolean | null {
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// Check <meta name="color-scheme" content="dark">
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const meta = document.querySelector<HTMLMetaElement>('meta[name="color-scheme"]')
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if (meta) {
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const content = meta.content.toLowerCase()
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// "dark" or "only dark" → dark; "light dark" is ambiguous so skip
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if (content === 'dark' || content === 'only dark') return true
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if (content === 'light' || content === 'only light') return false
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}
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// Check the computed color-scheme CSS property on :root
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const rootStyle = window.getComputedStyle(document.documentElement)
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const colorScheme = rootStyle.getPropertyValue('color-scheme').trim().toLowerCase()
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if (colorScheme === 'dark' || colorScheme === 'only dark') return true
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if (colorScheme === 'light' || colorScheme === 'only light') return false
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return null
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}
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/**
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* Checks if the text color on the body is light, which implies a dark background.
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* @returns {boolean}
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*/
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function isTextColorLight() {
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const bodyStyle = window.getComputedStyle(document.body || document.documentElement)
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const textColor = bodyStyle.color
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const rgb = parseRgbColor(textColor)
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if (!rgb) return false
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// Light text has high luminance (e.g. white text on dark bg)
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const luminance = 0.299 * rgb.r + 0.587 * rgb.g + 0.114 * rgb.b
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return luminance > 180
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}
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/**
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* Checks the background color of major layout elements (<main>, #app, #root, etc.).
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* Many SPAs render into a container that may have its own dark background while
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* <body> remains transparent.
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* @returns {boolean}
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*/
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function isMainContentDark() {
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const selectors = ['main', '#app', '#root', '#__next', '[role="main"]']
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for (const selector of selectors) {
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const el = document.querySelector(selector)
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if (!el) continue
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const style = window.getComputedStyle(el)
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if (isColorDark(style.backgroundColor)) {
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return true
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}
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}
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return false
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}
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2025-09-29 16:33:15 +08:00
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/**
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* A comprehensive function to determine if the page is currently in a dark theme.
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* It combines class checking and background color analysis.
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* @returns {boolean} - True if the page is likely dark.
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*/
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export function isPageDark() {
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2025-12-17 14:18:28 +08:00
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try {
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2026-04-20 20:14:07 -04:00
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// Strategy 1: Check for common dark mode classes and data attributes
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2025-12-17 14:18:28 +08:00
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if (hasDarkModeClass()) {
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return true
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}
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2025-09-29 16:33:15 +08:00
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2026-04-20 20:14:07 -04:00
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// Strategy 2: Check CSS color-scheme property and meta tag
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const colorScheme = getColorSchemePreference()
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if (colorScheme !== null) {
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return colorScheme
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}
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// Strategy 3: Analyze the computed background color of <html>/<body>
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2025-12-17 14:18:28 +08:00
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if (isBackgroundDark()) {
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return true
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}
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2025-09-29 16:33:15 +08:00
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2026-04-20 20:14:07 -04:00
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// Strategy 4: Check background of major layout containers (<main>, #app, etc.)
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if (isMainContentDark()) {
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return true
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}
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// Strategy 5: Check if text color is light (implies dark background)
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if (isTextColorLight()) {
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return true
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}
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2025-09-29 16:33:15 +08:00
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2025-12-17 14:18:28 +08:00
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return false
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} catch (error) {
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console.warn('Error determining if page is dark:', error)
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return false
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}
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2025-09-29 16:33:15 +08:00
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}
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