title: CSS multiple backgrounds scrolling at different speeds
body: <p>I came across this website today and I was mystified: <a href="http://www.actionbutton.net/" rel="noreferrer">http://www.actionbutton.net/</a></p>
  
  <p>Is he using some kind of known technique for his backgrounds that scroll at a different rate and overlap each other. I looked at the source but am pretty confused. Does anyone know what the technique is called and how to learn it?</p>