I was slightly disappointed at the heavy use of sprite sheets (which seems less than "pure" css), but after looking closely there would be no way to get the gears right just relying on css transforms (i.e. rotation) because of the 3d and brushed metal look they wanted for the gears.

But yeah extremely impressive. I could do implement it if you gave me those sprite sheets and javascript easily enough, but wouldn't have any clue how to with css.