// ==UserScript==
// @name         New Userscript
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  try to take over the world!
// @author       You
// @match        https://ru.wikipedia.org/wiki/*
// @grant        all
// ==/UserScript==

(function() {
    'use strict';

    document.getElementsByClassName('mw-body')[0].style.backgroundColor = 'pink';
    document.getElementsByClassName('mw-body')[0].style.fontSize = '30px';
    document.getElementsByClassName('mw-wiki-logo')[0].style.backgroundImage = "url('https://upload.wikimedia.org/wikipedia/commons/thumb/9/96/Lavrentiy_Beria_%28close-up%29.jpg/200px-Lavrentiy_Beria_%28close-up%29.jpg')";
})();