user script body to set Gerrit fonts

set_gerrit_font.js

// ==UserScript==
// @name         Gerrit Fonts
// @namespace    https://gerrit.YOURDOMAINHERE.com
// @match        https://gerrit.YOURDOMAINHERE.com/*
// ==/UserScript==

'use strict';

(function() {

    const font = "MonoLisa";

    // Gerrit dynamically populates its window, and then populates _that_ with a ton of shadow DOMs.
    // Accordingly, we'll run this when the main DOM is modified to add all the shadow DOMs.
    MutationObserver = window.MutationObserver || window.WebKitMutationObserver;
    var observer = new MutationObserver((mutations, observer) => {

        // This code is tantamount to a war crime.
        document
            .querySelector("#app").shadowRoot
            .querySelector("#app-element").shadowRoot
            .querySelector("gr-diff-view").shadowRoot
            .querySelector("gr-diff-host").shadowRoot
            .querySelector("gr-diff").shadowRoot
            .styleSheets[0].addRule("*", 'font-family: "' + font + '" !important');
    });

    // Select the node that will be observed for mutations.
    // Generally, adding something to the root node would mean it run a lot;
    // but thanks to Gerrit's aggressive shadow-dom'ing it only runs ~three times.
    const targetNode = document.getRootNode();

    // Options for the observer (which mutations to observe)
    const config = { childList: true, subtree: true, attribute: true };

    observer.observe(targetNode, config);
})();