I've inspected the code of https://highlightjs.org/.
In between the ... i've found a suspicous class attribute assigned to a tag. For example:
<link class="codestyle" rel="stylesheet" href="/static/styles/default.css" disabled="">
Google and the MDN truned out to be not helpful. Instead the MDN didn't even list the class attribute as possible attribute for a tag.
Does it have any effect?