The html playground thing going on here makes me feel like a kid on neopets again. Delighting over a fancy cursor, or css trick somebody squeezed past the strict yet safe and structured filters on petpages.
Petpages were incredible... I feel like I could go on forever about them. They offered the user an empty space to use how they wanted, along with a short URL associated with the pet's name (neopets.com/~petname). I would never have been motivated to learn HTML/CSS if it weren't common practice to put high quality pets up for adoption and demand elaborate adoption applications.