This looks really interesting. Going to give it a play today. I'm interested in how you handle keyframe animations

EDIT I had a quick look through your CSS (which I think is built using Xpressive) overall I think it looks pretty good. Although you could definitely shave of 30% off by inlining some of the rules. For instance for margin:0 auto; you call margin-left:auto, margin-right:auto. The same applies for background, using the shorter version cuts files sizes dramatically