This userscript makes compass classes dark by changing their css to the colour without !important afterwards.

CompassSchoolDarkMode.js

// ==UserScript==
// @name         Make compass classes dark.
// @namespace    http://tampermonkey.net/
// @version      1.2
// @description  Because the css of compasses classes listing has "!important" in the 'background-color:' DarkReader won't work. This changes that.
// @author       CoderCowMoo
// @match        https://*.compass.education/
// @require      https://gist.github.com/raw/2625891/waitForKeyElements.js
// @icon         https://www.google.com/s2/favicons?domain=compass.education
// @grant        none
// ==/UserScript==

(function() {
    'use strict';
    waitForKeyElements(".x-cal-default", darkify);
    function darkify() {
        var classes = document.getElementsByClassName('activity-type-1');
        for(var i = 0; i < classes.length; i++) {
            classes[i].style["background-color"] = "rgb(220, 230, 244)";
        }
    }
})();