CSS media queries themselves don't have the capability to send any tracking information back, but the effects they cause absolutely do. Consider:

  @media (min-width: 600px) { .pixel { background-image: url("/pixel?width=600"); } }
  @media (min-width: 700px) { .pixel { background-image: url("/pixel?width=700"); } }

You could add as many of these media queries as you like to increase the resolution of your tracking. Combine this with the min-height media query and you can get the absolute size of the view port.

That's still more finite than what JS can report, and can be easily broken by browser prefetching. (And could have performance implications that could drive users away.)

Whilst it's better-than-nothing fingerprinting, it is still far less effective than JS having access to the window and height properties directly.

False: it is possible with just CSS [1][2] to track screen resolution, browser engine, fonts, mouse movements and inputs.

[1] https://github.com/jbtronics/CrookedStyleSheets

[2] https://github.com/maxchehab/CSS-Keylogging

Both those methods rely on the browser not prefetching certain resources, which they are absolutely allowed to prefetch.

So if a browser changes the prefetching algo, the method is immediately broken. (For example enabling network.predictor.enable-prefetch in Firefox).

It isn't an inherent weakness of CSS itself.