You can set an Id to the link

isarbjitgrewal — Tue, 22 Aug 2017 05:08:41 +0000

You can set an Id to the link tag and switch the css at runtime.

HTML

document.getElementById('buttonID').onclick = function () {
document.getElementById('theme_css').href = '../red.css';
};

You will have to modify

DominickLo — Fri, 30 Dec 2016 17:17:39 +0000

You will have to modify existing JavaScript either replace with skin file or just add comments on them.