Render TOC without JavaScript

[srid]

As for highlightToc, do we really need JavaScript? I see a NoJS solution here: https://codepen.io/davorsuljic/embed/vYgqKWe? (via the comments from https://css-tricks.com/sticky-table-of-contents-with-scrolling-active-states/ )

Originally posted by @srid in #504 (comment)

[TristanCacqueray]

I get the appeal, but this css is really advanced, not sure what's the benefit at that point. If I understand correctly, each heading needs it's own css to match the relevant doc section.