I've also been messing with some more obscure HTML/CSS stuff like "pointer-event" and "use map" to make things like the bookshelf and custom link areas for weirdly shaped images.
I'm really proud of the bookshelf design on XP.html. It uses grid boxes and custom book elements so the order of the books and shelves is 100% customizable!
There's always a deeper hole that you've never heard of with HTML and CSS, lolol