I think geoffschmidt's otherwise great explanation explained the score calculation a wrong-way around: checked score radio buttons start with zero height and when they get unchecked they grow to their 93px height.

I learned a few new things that were necessary to understand this:

1) States of radio inputs can be connected by name attributes and connected inputs can have an inverse state to each other.

2) Transition effects can be connected to checked/unchecked states (at least with "all" property)

3) Using a wrapper div with overflow:hidden you can create "a window" to a larger content that moves "behind" the window. I've seen this in some scroller effects, but as my CSS skills are quite bad, I couldn't yet write one without googling for some help.