Edit
While the solution below worked locally, uploading to Github Pages broke it all. So it’s still not fixed.
Original reply
OK, I’ve found the solution.
Unlike the initial Jekyll link I provided, there is another Jekyll guide which says you need to have a stylesheet at _css/syntax.css
This blog shows you how and where to put everything, along with a stylesheet you can use.
For reference:
- Add syntax highlighter CSS file as css/syntax.css to your existing or newly generated Jekyll site
- Load CSS inside of a corresponding layout file (e.g. _layouts/default.html):
<link href="/css/syntax.css" rel="stylesheet">