Earlier quoted context omitted.
Yes, CSS has an unhelpful definition of pixels, which AFAICS is almost universally ignored. No doubt it was well-intentioned, but in the real world, pixels have fixed sizes and display devices do not have infinite resolutions. The difference between professional quality web design and an amateurish mess can be as simple as paying attention to the real pixel grid that your beautiful vector icon/font/whatever will be d…
> which AFAICS is almost universally ignored. Safari on iPhone uses that definition (that's the whole "resolution doubling" thing, in a nutshell). Gecko uses that definition, including on mobile devices. In fact, that definition is almost universally _used_ in cases where it matters (i.e. high-dpi displays). > Given that CSS also recognises length units such as pt Which are nowadays defined in terms of CSS px, becaus…
That's my point, though: no-one is really implementing CSS-px. What they're doing is implementing approximations, like doubling everything up on a high-dpi screen because the pixel pitch is roughly twice what you get on a typical desktop monitor, which is close enough to be workable.
If browsers implemented CSS-px as specified, then on all the monitors in front of me, the text on most pages I have open right now would look the same size in Firefox, and not noticeably smaller on some monitors than others. Also, all those beautiful, crisp n-pixel borders on mobile-friendly sites would look terrible (because they would be rendered with different degrees of fuzziness due to the antialiasing on different mobile devices) and everyone's photographs on Facebook would be blurry. Of course, that's a silly idea, and no browser actually does it (other than when zooming).
Most of the major mobile browsers (possibly all by now) support restricting the viewport and zoom so you can match your site to real, physical screen properties instead of whatever virtual viewport size they pretend to have by default. IME, a fairly high proportion of mobile-specific and responsive pages now start by switching this on. No-one's going to change this functionality any time soon, because vast numbers of mobile-optimised sites would immediately break. Fortunately, that means we can go into real-physical-dimensions modes and then use media queries to select an appropriate layout (including text sizes) for smaller, high-dpi devices as part of a design, without sacrificing precision in cases where the time and money is there to work on the fine details for best results on that kind of device.