I actually thought about that in my initial reply to the OP, but discarded it since the point seemed to be to help new monks adjust to the trolls - which would be the very same people who wouldn't know to change their CSS. If anything, we'd have to go the other way to help the new monks: add this to the CSS of new users while experienced ones could go and update their CSS to remove it. Not a lot better in my estimation, but still would be there to advise the new monks.

That said, it still doesn't quite help in cases where a troll may have multiple accounts - one for trolling, and one for reading (where they'd see their own highlights and get their kick from it). Not that any solution would do this perfectly, but a small barrier to entry may still be quite helpful here.