What did StackExchange use to build to popup like dialog when you click StackExchange in the Top Left?

On stackoverflow, when you click "StackExchange" in the top left, it opens a popup like dialog. Anyone know what they used to create that or what type of jQuery plugin makes such a开发者_C百科 UI?

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This doesn't require a plugin per se. You can just fade a div containing the content with a scrollbar when you click the link. Check out Firebug, it's great for determining how things are built.

For this link particularly, it looks like most of the work is the CSS.