nice. I've actually used this kind of CSS technique a few times to mimic collapsibles and overcome the fact that you can't nest collapsibles.
This is nice. I really hope we'll get this automatically in all themes soon.
But one thing: Why not let me choose (as an admin for all users, or as a user for just me) to use the more common and well known MediaWiki syntax? It's so confusing with all these different syntaxes. Let me at least have the option to use the one that I most likely know a little already. (even better could be to let me choose from a list of the most common syntaxes) That would be very helpful!