あとこれか
// ==UserScript==
// @name Meta theme
// @namespace http://tampermonkey.net/
// @version 0.1
// @description try to take over the world!
// @author You
// @include *
// @grant none
// ==/UserScript==

const theme = document.querySelector('meta[name="theme-color"]');
if (theme) theme.remove();
const meta = document.createElement('meta');
meta.name = 'theme-color';
meta.content = '#000000';
document.head.appendChild(meta);


https://i.imgur.com/2IALNAu.jpg
https://i.imgur.com/een2zxO.jpg