System light/dark theme preference for Vorapis V3 - oneshotted with claude, might nuke your settings =)

v3systemtheme.user.js

// ==UserScript==
// @name         V3 - System theme
// @namespace    http://tampermonkey.net/
// @version      1.0.0
// @match        *://*.youtube.com/*
// @description  Sets dark mode in V3 based on system preference
// @license      MIT
// @grant        none
// ==/UserScript==

(function() {
  const getDarkMode = () =>
    window.matchMedia?.('(prefers-color-scheme: dark)').matches ?? true;

  const updateTheme = () => {
    const settings = localStorage.getItem('v3_local_db');
    if (!settings) return;

    try {
      const parsed = JSON.parse(settings);
      parsed.config?.db?.yt && (parsed.config.db.yt.DARK_MOD = getDarkMode());
      localStorage.setItem('v3_local_db', JSON.stringify(parsed));
    } catch {
      console.error('Could not parse or update theme settings.');
    }
  };

  window.matchMedia?.('(prefers-color-scheme: dark)')
    .addEventListener?.('change', updateTheme);

  updateTheme();
})();