添加到油猴脚本即可 
// ==UserScript==
// @name         豆包网页版自动主题
// @description  豆包网页版根据系统自动切换浅色/深色主题
// @version      1.1
// @author       doubao
// @match        https://*.doubao.com/*
// @grant        none
// @run-at       document-start
// ==/UserScript==

(() => {
  const mediaQuery = window.matchMedia('(prefers-color-scheme: dark)');
  const getTheme = () => mediaQuery.matches ? 'dark' : 'light';

 ...