Well I saw a pretty nice mockup on Dribbble and decided to make it for fun. It didn't include a mobile/responsive solution, so I came up with my own.
Check the demo.
This is a pure CSS solution - it uses the :target selector for changing states.
Find more about :target on MDN.
This is neat, as it also can be bookmarked in both states, and browser buttons work too.
Grab the code on GitHub.