Twitter Auto Dark Mode

twitter-darkmode.user.js

// ==UserScript==
// @name     Twitter auto darkmode
// @version  1
// @grant    none
// @match    *://twitter.com/*
// ==/UserScript==

window.matchMedia('(prefers-color-scheme: dark)').addEventListener('change', e => {
  const isDarkMode = e.matches ? 1 : 0;
  document.cookie = `night_mode=${isDarkMode};path=/;domain=.twitter.com;secure`;
});

after rebrand

// ==UserScript==
// @name     Twitter auto darkmode
// @version  1
// @grant    none
// @match    *://twitter.com/*
// @match    *://x.com/*
// ==/UserScript==

window.matchMedia('(prefers-color-scheme: dark)').addEventListener('change', e => {
  const isDarkMode = e.matches ? 1 : 0;
  document.cookie = `night_mode=${isDarkMode};path=/;domain=.twitter.com;secure`;
  document.cookie = `night_mode=${isDarkMode};path=/;domain=.x.com;secure`;
});

If you prefer the dark mode to be lights out instead of dim, change this line:

const isDarkMode = e.matches ? 1 : 0;

to this:

const isDarkMode = e.matches ? 2 : 0;