exercism.js

// ==UserScript==
// @name         Exercism completed in green
// @namespace    http://tampermonkey.net/
// @version      0.1
// @author       You
// @match        https://exercism.io/my/tracks/*
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    var css = '[data-status="Completed"] { background: #85e285 !important; } [data-status="Completed"] .hover { display: inline !important; } [data-status="Completed"] .normal { display: none !important; }';

    var style = document.createElement('style');
    document.head.appendChild(style);

    style.type = 'text/css';
    style.appendChild(document.createTextNode(css));
})();