Dark mode rules, okay!
// ==UserScript==
// @name John Lewis dynamic favicon supporting dark mode
// @namespace http://tampermonkey.net/
// @version 0.1
// @description Dark mode rules, okay!
// @author Beazley
// @license GNU GPLv3
// @match https://*.johnlewis.com/*
// @icon data:image/svg+xml;utf-8,%3Csvg viewBox='0 0 144 92' xmlns='http://www.w3.org/2000/svg'%3E%3Cstyle%3E:root %7Bfill: %23000;%7D@media (prefers-color-scheme:dark)%7B:root %7Bfill: %23fff;%7D%7D%3C/style%3E%3Crect x='52' width='92' height='92'%3E%3C/rect%3E%3Crect x='33' width='13' height='92'%3E%3C/rect%3E%3Crect x='16' width='8' height='92'%3E%3C/rect%3E%3Crect width='4' height='92'%3E%3C/rect%3E%3C/svg%3E
// @grant none
// ==/UserScript==
(function() {
'use strict';
const svg = "data:image/svg+xml;utf-8,%3Csvg viewBox='0 0 144 92' xmlns='http://www.w3.org/2000/svg'%3E%3Cstyle%3E:root %7Bfill: %23000;%7D@media (prefers-color-scheme:dark)%7B:root %7Bfill: %23fff;%7D%7D%3C/style%3E%3Crect x='52' width='92' height='92'%3E%3C/rect%3E%3Crect x='33' width='13' height='92'%3E%3C/rect%3E%3Crect x='16' width='8' height='92'%3E%3C/rect%3E%3Crect width='4' height='92'%3E%3C/rect%3E%3C/svg%3E"
let link = document.querySelectorAll("link[rel~='icon']")
if (link.length > 0) {
link.forEach(l => l.href = svg)
} else {
link = document.createElement("link")
link.rel = "shortcut icon"
link.type = "image/svg+xml"
link.href = svg
document.getElementsByTagName("head")[0].appendChild(link)
}
})();