Andrew pointed out webrender yesterday. A new rendering technology for CSS from the folks that are reinventing C++ with Rust and browsers with Servo. There is a great talk about this technology by Patrick Walton. It is worth watching in its entirety, but 26 minutes in has the examples. The key insight is that using a retained mode approach to rendering CSS is much more efficient than an immediate mode approach. The latter is what browsers have been using thus far and makes sense for the
canvas element (which offers an immediate mode rendering API), but is apparently suboptimal when talking to the GPU. Patrick mentioned this was pointed out back in 2012 by Mark J. Kilgard and Jeff Bolz from NVIDIA in a paper titled GPU-accelerated Path Rendering:
We believe web browsers should behave more like video games in this respect to exploit the GPU.