This lets you provide an implementation for a CSS feature that is perhaps not yet implemented by browsers, or maybe never will be. You could always do this wit

This lets you provide an implementation for a CSS feature that is perhaps not yet implemented by browsers, or maybe never will be. You could always do this with Javascript, and some people have been. See: https://philipwalton.github.io/polyfill/ https://philipwalton.github.io/polyfill/ But this lets you do it in a less hacky, and especially, more performant way. The author of that JS CSS polyfill library above actually wrote in 2016 how that approach was proving a bad idea, and the right way to do this was the houdini API... I guess we've been waiting for it since 2016? This is the first I had heard of it. https://philipwalton.com/articles/the-dark-side-of-polyfilling-css/ https://philipwalton.com/articles/the-dark-side-of-polyfilli...