For anyone looking for an easier way to implement this, I’ve got it working on my Ghost instance by adding the following to the Header:
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/prism/1.29.0/plugins/toolbar/prism-toolbar.min.css" integrity="sha512-Dqf5696xtofgH089BgZJo2lSWTvev4GFo+gA2o4GullFY65rzQVQLQVlzLvYwTo0Bb2Gpb6IqwxYWtoMonfdhQ==" crossorigin="anonymous" referrerpolicy="no-referrer" />
And the following to the Footer:
<script src="https://cdnjs.cloudflare.com/ajax/libs/prism/1.29.0/plugins/toolbar/prism-toolbar.min.js" integrity="sha512-st608h+ZqzliahyzEpETxzU0f7z7a9acN6AFvYmHvpFhmcFuKT8a22TT5TpKpjDa3pt3Wv7Z3SdQBCBdDPhyWA==" crossorigin="anonymous" referrerpolicy="no-referrer"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/prism/1.29.0/plugins/copy-to-clipboard/prism-copy-to-clipboard.min.js" integrity="sha512-/kVH1uXuObC0iYgxxCKY41JdWOkKOxorFVmip+YVifKsJ4Au/87EisD1wty7vxN2kAhnWh6Yc8o/dSAXj6Oz7A==" crossorigin="anonymous" referrerpolicy="no-referrer"></script>
Which looks like this:
