I love classless CSS for rapid hand prototyping. LLMs are making this increasingly less necessary, but it's still great for creating tiny, performant CSS pages and some of the smaller ones can even be inlined in fewer bytes than it takes to make a 2nd round trip to the server to check if the asset has been updated. This is one of my secret weapons for creating web apps that load and render so fast you can feel the difference!
https://dohliam.github.io/dropin-minimal-css/
But might be due a revival on the shoulders of LLMs.