How? Admittedly my knowledge of CSS is dated, but without scripting enabled you can't set cookies, make auto server request, or even auto set an external CSS file (that could be served and counted)..
Its not something I've considered before and i am genuinely curious how this would work.
You can make server requests by loading images and fonts. Browsers only load those resources they actually need, so there's lots of opportunities for conditionally triggering requests. Media queries for window size, fallback fonts to check installed fonts, css feature checks to make guesses at the browser type, ...
Its not something I've considered before and i am genuinely curious how this would work.