I haven't even done stylesheets for the standard different media before (screen/print/etc) but this looks super neat.
You can change the style by how big the screen is; that opens up a whole lot of possibilities, especially for a webgame where the interactive parts of the game really need to stay on the screen.
For example, deciding not to use images when the screen is too small.
It's simple stuff. And probably not new to you. But cool.