Bilibili Auto Theme

Sync Bilibili theme_style cookie with system dark/light mode

You will need to install an extension such as Tampermonkey, Greasemonkey or Violentmonkey to install this script.

You will need to install an extension such as Tampermonkey to install this script.

You will need to install an extension such as Tampermonkey or Violentmonkey to install this script.

You will need to install an extension such as Tampermonkey or Userscripts to install this script.

You will need to install an extension such as Tampermonkey to install this script.

You will need to install a user script manager extension to install this script.

(I already have a user script manager, let me install it!)

You will need to install an extension such as Stylus to install this style.

You will need to install an extension such as Stylus to install this style.

You will need to install an extension such as Stylus to install this style.

You will need to install a user style manager extension to install this style.

You will need to install a user style manager extension to install this style.

You will need to install a user style manager extension to install this style.

(I already have a user style manager, let me install it!)

// ==UserScript==
// @name         Bilibili Auto Theme
// @namespace    https://bilibili.com/
// @version      1.0.1
// @description  Sync Bilibili theme_style cookie with system dark/light mode
// @match        *://*.bilibili.com/*
// @run-at       document-start
// @grant        none
// @license      MIT
// ==/UserScript==

(function () {
  const COOKIE_KEY = "theme_style";
  const DARK_QUERY = "(prefers-color-scheme: dark)";

  const getCookie = (key) =>
    document.cookie.match(new RegExp(`(?:^|; )${key}=([^;]*)`))?.[1];

  const setThemeCookie = (theme) => {
    document.cookie = `${COOKIE_KEY}=${theme}; domain=.bilibili.com; path=/; max-age=31536000; secure`;
    console.log("[Theme Sync] Cookie updated:", theme);
  };

  const updateTheme = () => {
    const isDark = window.matchMedia(DARK_QUERY).matches;
    const systemTheme = isDark ? "dark" : "light";
    const currentTheme = getCookie(COOKIE_KEY);

    if (currentTheme !== systemTheme) {
      setThemeCookie(systemTheme);
      // recommended small delay to ensure cookie applied before reload
      setTimeout(() => window.location.reload(), 100);
    }
  };

  // Initial sync
  updateTheme();

  // Watch for system theme changes
  window.matchMedia(DARK_QUERY).addEventListener("change", updateTheme);
})();