Very few CSS animations are cheap in performance terms. Anything that affects HTML layout (AKA reflow) is bad. The more complex your page the worse the performance hit.

But – these four are apparently particularly cheap (and often GPU assisted):

  • translate(_n_px, _n_px);
  • scale(n);
  • rotate(_n_deg);
  • opacity: 0…1; (edited)
Read more:

developers.google.com/…/design-and-ux/…/animations-and-performance
* html5rocks.com/…/high-performance-animations/