The idea of using CSS-triggered requests for analytics was really cool to me when I first encountered it. One guy on twitter (no longer available) used it for

The idea of using CSS-triggered requests for analytics was really cool to me when I first encountered it. One guy on twitter (no longer available) used it for mouse tracking: overlay an invisible grid of squares on the page, each with a unique background image triggered on hover. Each background image sends a specific request to the server, which interprets it! For fun one summer, I extended that idea to create a JS-free "css only async web chat": https://github.com/kkuchta/css-only-chat https://github.com/kkuchta/css-only-chat