Why do you think a client should have to download a dark mode CSS separately? Have you put any thought into why that is treated as a separate request, rather than a function of an existing page that could be switched between offline without any acknowledgement sent from the client?

Web standards have been butchered to force these constant validation measures for the sole purpose of telemetry/spyware. A client should be able to render a web page however the fuck it wants and the server that sent the page should be none the wiser.

And what of things like battery status? That has no legitimate purpose at all. No web site is going to change its behavior in response to your battery status, but current charge % and battery wear stats alone are enough to perfectly distinguish your mobile device from anyone else that you would be sharing a IP address with.