[mbirth]

Embedded CSS circumvents proper caching of the CSS. Also, with HTTP/2 your client can download several resources in one transaction. So, it shouldn’t make much of a difference with CSS embedded or separate. Just, that embedded CSS has to be loaded over and over again whereas a separate file can be cached and reused from the local cache.

[MrJohz]

Caching is only relevant if you think your site is going to be visited by the same person often enough that the cache is worthwhile. If the assets are small that HTTP overhead is non-negligible, and if your CSS would get few enough cache hits, then you're often better off just inlining stuff.

HTTP/2 does not change this equation much. Server Push is dead, and bypasses caching anyway. Early Hints can help if configured correctly, but still require the client to make the request roundtrip to fetch that asset.