CSS exfiltration example

stylesheet.css

.pointer {
  background-image: url('/some/url/pointer=none')
}

// Coarse (touchscreen)
@media (any-pointer: coarse){
  .pointer {
    background-image: url('/some/url/pointer=coarse')
  }
}

// Fine (mouse)
@media (any-pointer: fine){
  .pointer {
    background-image: url('/some/url/pointer=fine')
  }
}