For Android, people recommend using dp (density independent pixels) measurements for UI elements, and there are conventions that exist such as using 48dp for a
48dp
In CSS3 it may be more accurate to say that the web doesn't have Android's px. The spec for CSS3's px says this:
px
pixels; 1px is equal to 1/96th of 1in
px might be the measurement you want, in the future.