This is a nice 404 page with CSS animations. I created it for one of my answers on toster.ru. I was inspired by GIF animation from dribbble, but unfortunately I don’t remember the name of its author. This animation is pretty simple and lightweight - only four circles, twelve numbers and ‘Oops….’ message.
Looking for a step-to-step tutorial without mathematics?
Check out my article about WebGL shaders with examples adapted especially for UI developers (in Russian)!