// ==UserScript==
// @name         Whatsapp Native Dark Theme
// @namespace    http://web.whatsapp.com/
// @version      1.00
// @description  Adds "dark" class to the Whatsapp Web document to enable its native dark theme
// @author       Jair Jaramillo
// @match        *://web.whatsapp.com/*
// @grant        none
// @run-at       document-end
// ==/UserScript==
window.addEventListener ("load", pageFullyLoaded);
function pageFullyLoaded () {
document.getElementsByTagName("body")[0].classList.add('dark');
}