Juriy Zaytsev hat einen sehr ausführlichen Post über CSS Profiling und Performance geschrieben.
The fastest rule is the one that doesn’t exist. There’s a common strategy to combine stylesheet “modules” into one file for production. This makes for one big collection of rules, where some (lots) of them are likely not used by particular part of the site/application. Getting rid of unused rules is one of the best things your can do to optimize CSS performance, as there’s less matching to be done in the first place. There are certain benefits of having one big file, of course, such as the reduced number of requests. But it should be possible to optimize at least critical parts of the app, by including only relevant styles.
This isn’t a new discovery by any means. Page Speed has always been warning against this. However, I was really surprised to see just how much this could really affect the rendering time. In my case, I shaved ~200-300ms of selector matching — according to Opera profiler — just by getting rid of unused CSS rules. Layout and paint times went down as well.
Die meisten Tips beziehen sich zwar auf große, komplexe One-Page-Apps, aber spannend ist das trotzdem.