Div that follows scroll (not position:fixed)

[ptytb]

I found it sometime ago and now I can't. I want to find something like the shopping cart at the apple store, it's a div thats not positioned absolute nor fixed, for instance, let's say it's at the center of the screen, and only when you scroll down it follows the scroll only to not disappear, when it reaches the border of the browser header...I'm not sure If i'm being clear. I've searched but all I found is the css position fixed stuff.Can you help me with a link or something?Best Regards