Drop -webkit-box-sizing

[BBosman]

All supported browsers support it without the -webkit prefix, so we should drop it.

http://caniuse.com/css3-boxsizing

[cvrebert]

20% of Android users are still on v2.3 "Gingerbread", whose non-Chrome stock browser requires the prefix. The Android stock browser is indeed not officially supported, but I still fear the number of issues that people might file as a result of this change.

[zlatanvasovic]

@cvrebert 20% of Android users are still on Gingerbread, but 19.99% of those users (including me, but I have also newer phone) migrated to Firefox, Opera or something else. 😉

Bigger problem is Safari 5, on older Macs.

[BBosman]

Normalize.css doesn't use any of the prefixes that 2.3 requires and there are places in the bootstrap code itself where we're not using them (box-shadow, background-clip and background-size need to be prefixes for example).

So support for 2.3 is already flaky at best.

[mdo]

Indeed we don't have -webkit prefixes for many of our visual CSS properties like box-shadow. However, the box model is a much more important thing to keep intact for the maximum number of users, no matter what. We don't officially support Android 2.x, but we do everything we can to help.

For now, we'll leave it.