I'm getting that too on Chrome 34 and Opera 20. I'm on Windows 8.
It's a hack on display refresh rate. I think your monitor might have a higher display rate than 60 Hz. Try on a different device.
Normally it should generate 4 different rotating circles.
That's really tight. I'm very excited about the idea of everything becoming dynamic and code-oriented. Going into Photoshop feels like entering the dark ages these days vs. change-on-the-fly already-in-the-browser CSS3.