Tests layout styles. First up...
Lays children out horizontally, stretched vertically. Note that children must have no space between them in the html, as they are inline-blocks...
width: 20%;
Lays children out vertically, stretched horizontally
height: 60%;
Centres children of unkown dimensions
Opera: fails to support box-pack: center;
FF: Allows children to push the box wider than defined - in WebKit they simply overflow, allowing you to hide them and whatnot. FireFox, frustratingly, breaks display: box; if you try applying overflow, positioning, float, and probably more. Use with caution.