Photoshop Help: That glossy widget look

I consider myself fairly good with photoshop, having used it since version 1.5. However, I am by no means a hardcore graphics guy.

I'm getting frustrated trying to get that "glossy" look that all the widgets are using now. I'd like to use that to section off some larger portions of a web site.

There are two pictures below--the first is an example of what I'm trying to accomplish. The second is the background color I'm going to use. I'd like to get a nice glossy black "wet" square, like someone spilled water or something. Very dark and very wet.

Can somebody give me the photoshop steps to do this? I have googled, but all the tutorials I try don't quite look right when I do them. Thanks!
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