Centering content of unknown dimensions (and since the user is ultimately in control of font size this happens often) vertically is surpringly difficult to do i

Centering content of unknown dimensions (and since the user is ultimately in control of font size this happens often) vertically is surpringly difficult to do if you want to support legacy browsers. It's a common pain point. There are others, but this one is particularly vexing (esp. to newcomers to CSS) because it seems, at first glance, like it should be easy.