@Nancy, you might need to make your browser's screen wider to see the effect the OP is looking at. Half of the page scrolls up, the other half down, while backgrounds change behind the scrolling bits.
Neat effect, but it doesn't break down well in narrower screens and just looks like a long page of 100% width <div> tags that have background-images set.
Oh. I see the effect now that I've zoomed out in my desktop browser. It's very slick but mobile devices probably won't see it that way.