umm ok but why not box-sizing? html{box-sizing:border-box} *,:after,:before{box-sizing:inherit}
Personally I think a much better question is why change the box-sizing? I’d call it out of scope for something like this. Very seldom have I encountered a situation where I actually want border-box rather than content-box; there are normally better ways of doing things. (Truth to tell, I’ve wanted padding-box more often than border-box in recent times, but only Firefox supports it.) Ideally calc() can be used too; it…
Because the default content-box is a pain in the ass to work with, so to be able to use border-box all the time is a good thing: http://www.paulirish.com/2012/box-sizing-border-box-ftw/.