The top one is two divs on top of each other. So the front one holds the animation and the backone holds the background.
But we can't double all the divs because it would make scrolling the map slow.
This must be a bug in chrome, can't see how it can be any other way. There is nothing wrong with CSS, I've checked it a bunch of times and it runs in every other browser. Would be good to figure out what triggers the bug and report to google.