Userscript to force certain fonts

custom-font.user.js

// ==UserScript==
// @name         Custom font
// @namespace    polv/wanikani
// @version      0.1
// @description  Custom font for a CSS selector
// @author       You
// @match        https://www.wanikani.com/*
// @grant        none
// ==/UserScript==

(function() {
    'use strict';

    // Font list from Jisho.org
    // Or specific font, such as Biz UDPMincho;
    // Or css values, such as serif or unset;
    document.head.append(Object.assign(document.createElement('style'), { textContent: `
    [lang="ja"] {
      font-family: "Source Han Sans", "源ノ角ゴシック", "Hiragino Sans", "HiraKakuProN-W3", "Hiragino Kaku Gothic ProN W3", "Hiragino Kaku Gothic ProN", "ヒラギノ角ゴ ProN W3", "Noto Sans", "Noto Sans CJK JP", "メイリオ", Meiryo, "游ゴシック", YuGothic, "ＭＳ Ｐゴシック", "MS PGothic", "ＭＳ ゴシック", "MS Gothic", sans-serif;
    }
    ` }));
})();