Ugh, too clever for my taste. I would hate to edit icons that are a mish-mash of CSS backgrounds, rotated boxes, and border-radius'ed edges, and to boot, based entirely on pseudo-elements. (Current web dev tools like Web Inspector in Chrome/Safari, etc. aren't well built for examining pseudo-elements.) This CSS uses ~3-4 pseudo-elements per icon. It's clever for doing that to preserve the markup and avoiding JS, but it's hard to understand. Maybe it would help to comment the CSS so designers can see that "this is the handle of the trash can, this is the left side of the heart," etc., since :after and :before are hacked far beyond having any semantic meaning.