You're absolutely right.
The guidelines I outlined don't work well if retrieving the CSS requires a subsequent DNS lookup. One could argue that serving CSS from the host that serves the HTML is a good idea, but there are other tradeoffs involved.
The guidelines I outlined don't work well if retrieving the CSS requires a subsequent DNS lookup. One could argue that serving CSS from the host that serves the HTML is a good idea, but there are other tradeoffs involved.
The main thing I'd like to see in guides like this would be some general advice about how to measure this kind of thing (e.g. browser dev tools) and, more importantly, how to avoid some of the common confounds like local caches when measuring using a tool like WebPageTest.org.