I’ve made two versions of it.
This one - http://codepen.io/Shoggoth/pen/OXGkXB - works great in Opera (at least, for me), okay in Chrome and it just works in Firefox but not as intented. Also, be aware, it’s traffic-heavy.
This one works everywhere - http://codepen.io/Shoggoth/pen/mEYGRp but I couldn’t animate the change of a background gradient.