.... displays an full-width image and nav bar that starts out below the top of screen and "sticks" to top after you start scrolling down.

Anyone know how to replicate this?
My question is why would you want to do this? It's ugly in my opinion and just confuses the page display. Have a sticky navbar by all means but don't have it jump up and down the screen dependant on the scrolling, just have it stick to the top of the page. Appears to me it's one of these "Just because you can do it, do you really have to do it?" type of effects.