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It's some javascript that does it along with CSS. The javascript starts it moving once you scroll then the css does the movement until the top then the JS parks it.
CSS:
Code:
position:fixed;
bottom:0px;
right:0px;

Adjust as necessary to get it to wherever you want it.
 
Looks like Apple's implementation uses position:absolute. I would recommend dmmcintyre3's method as the reason Apple doesn't use position:fixed is that it would cover up the top menu.
 
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