CSS only toggle (no js!)

A simple toggle I worked on today for a web project our team is working on. Uses only CSS3 with transitions, no javascript.

Thanks to @Derek Marler for help on the design.

Update! I wrote a simple blog post (and created a codepen) to show how this was done. Check it out:
http://petelada.com/2015/01/31/css-only-toggle.html