Added non-WebKit prefixed version of CSS animation; hide scrollbars

So I found this gem today and wanted to see it as the genius author @blakeeb intended. 

I added the non-WebKit prefixed CSS rules since most modern browsers support those now.

Tested in Firefox 31, Internet Explorer 11, and Chrome 36 (which can't even render the emoji) - the animations and background work fine, and the scrollbars are no longer displaying during the animation.