Showing & Hiding Panels with HTML and CSS

I’ve always loved web apps that use little panels that animate in from the sides as a way to show and hide content, settings, or other components of a web page. We used them a couple of times in Tweeter Fall, so I figured I’d share my way of doing them. I wanted to try doing this without any libraries to start, using only HTML5, CSS3 and as little JavaScript as possible, which will work for most browsers, but not all. Once we get it working with the latest stuff, I’ll go back and make the necessary modifications to get it to work across all browsers.