This is very cool. I have no idea how this one work. I'm guessing most of the magic is in the box shadow?
If you inspect what's getting rendered, there's a sprite map expressed as a data URI that's doing most of the heavy lifting.
I don't understand how so few lines can produce so much different things.
And clicking on the background will just create a new random (?) background!
It seems that the aliases are doing a lot of work