It isn't supported out of the box. You could further process ddoc output, I had
something working nicely by spitting out xml instead of html and then using
xquery to generate the docs, but am too much pressed for time to finish it.

A more lightweight approach is to insert a css class though a custom ddoc macro:

API_GROUP = <span class="$0"/>

>From there you can use css selectors for styling. I'm not sure how far you can
get with just css. A wee bit of jquery might help. It will be pretty awkard
anyway I suppose.