The power of pure CSS
Enter Stu Nicholls and his CSS Playground. First example of something that will make you think “that’s just CSS??” is the amazing puzzle. Give it a try. And go “ooooh, that’s clever”.
The major way of implementing some form of interactivity through pure CSS is with the :hover directive, and the major thing standing in the way of this is that IE doesn’t support :hover on anything other than links. Nonetheless, some impressive things are possible: see Stu’s photo gallery for one example. It’s not that these techniques are revolutionary, it’s more that they do exist and can be exploited to add some neat things to your sites without any scripting at all.