r-eu4-styles.userscript

// ==UserScript==
// @name         /r/EU4 styles
// @namespace    https://github.com/birjolaxew/r-EU4-styles
// @version      1.0
// @description  Add custom CSS style to /r/EU4
// @author       birjolaxew
// @match        https://www.reddit.com/r/eu4/*
// @run-at       document-body
// @grant        none
// ==/UserScript==

(function() {
  'use strict';
  console.log("Injecting /r/EU4 styles");
  [...document.querySelectorAll("link[ref='applied_subreddit_stylesheet']")].forEach($link => $link.parentNode.removeChild($link));
  const $link = document.createElement("link");
  $link.setAttribute("rel", "stylesheet");
  $link.setAttribute("type", "text/css");
  $link.setAttribute("ref", "applied_subreddit_stylesheet");
  $link.setAttribute("title", "applied_subreddit_stylesheet");
  $link.href = "https://www.reddit.com/r/birjolaxewssubreddit/stylesheet";
  document.head.appendChild($link);

  const img = new Image("https://raw.githubusercontent.com/birjolaxew/r-EU4-styles/master/resources/shield_logo.png");
  document.addEventListener("DOMContentLoaded", () => {
    const $logo = document.getElementById("header-img");
    $logo.src = "https://raw.githubusercontent.com/birjolaxew/r-EU4-styles/master/resources/shield_logo.png";
    $logo.width = 114;
    $logo.height = 114;
  });
})();