Nolan Lawson did a good write up comparing browsers - https://nolanlawson.com/2022/06/22/style-scoping-versus-shadow-dom-which-is-fastest/ https://nolanlawson.c

Nolan Lawson did a good write up comparing browsers - https://nolanlawson.com/2022/06/22/style-scoping-versus-shadow-dom-which-is-fastest/ https://nolanlawson.com/2022/06/22/style-scoping-versus-shad... His talk here is also a great deep dive - https://nolanlawson.com/2023/01/17/my-talk-on-css-runtime-performance/ https://nolanlawson.com/2023/01/17/my-talk-on-css-runtime-pe...