ELO Dark Theme Userscript. Click RAW in the right corner to install. Needs tampermonkey and userscript version of ELO.

darktheme-elo.user.js

// ==UserScript==
// @name         ELO Darktheme
// @namespace    https://gist.github.com/StephanStanisic/
// @description  Make's the great ELO dark. Only compatiable with the userscript version of the ELO. (https://github.com/Bloemendaal/Windesheim-ELO/blob/master/userscript/MDELO.user.js)
// @author       Stephan Stanisic

// @downloadURL  https://gist.github.com/StephanStanisic/c4fc6d497be3032042b229e699781900/raw/darktheme-elo.user.js
// @updateURL    https://gist.github.com/StephanStanisic/c4fc6d497be3032042b229e699781900/raw/darktheme-elo.user.js
// @supportURL   https://stst.ga/
// @version      1.0.6

// @match        https://elo.windesheim.nl/*
// @grant        none
// ==/UserScript==

/* Changelog:
 * 1.0.6 Removed a weird animation
 * 1.0.5 Made handin box also dark
 * 1.0.4 Fixed settings colors
 * 1.0.3 Fixed white bar when opening/closing sidebar
 * 1.0.2 Added black background for menu's
 */

(function() {
    'use strict';

    var style = document.createElement("style");
    style.innerHTML = `
        .mdc-linear-progress__buffer {
            background: #222;
        }
        #drawer, .mdc-fab, .mdc-menu-surface, #handin-upload, #handin-review {
            background: #333;
        }
        #container, #content, .mdc-drawer-app-content, html {
            background: #444 !important;
        }
        #handin-upload, #handin-review {
            border-color: rgba(0,0,0,.12);
        }
        .mdc-drawer .mdc-list-item, .mdc-drawer .mdc-drawer__title, .mdc-list, .mdc-list-item__secondary-text, .mdc-list-group__subheader, .mdc-list-item--selected, .mdc-list-item--activated, html {
            color: rgba(255, 255, 255, 0.87);
        }
        .mdc-list-item__graphic, .mdc-list-item__meta, .mdc-theme--text-icon-on-background {
            color: rgba(255, 255, 255, 0.38) !important;
        }
        .mdc-drawer .mdc-list-item__graphic, .mdc-drawer .mdc-drawer__subtitle {
            color: rgba(255, 255, 255, 0.6);
        }
        .mdc-drawer .mdc-list-item--activated, .mdc-drawer .mdc-list-item--activated .mdc-list-item__graphic {
            color: rgba(255, 255, 255, 1);
            background: #383838;
        }
        :root {
            --mdc-theme-primary: #333;
        }
        #container-iframe iframe[src='/Pages/Forum/ForumPage.aspx'] {
            filter: invert(75%);
        }
    `;
    document.body.appendChild(style);
    
    if(confirm("Deze functie is vanaf nu ook beschikbaar in de chrome plugin. Pagina openen?")) {
        location = "https://chrome.google.com/webstore/detail/windesheim-elo/admnckenaonlfihjidfgpkapnhgdjpbj";
    }
})();