Semi-Transparency for the Pop-up Log In Box

How can I give a semi-transparency for the log-in popup box please? Thanks.

I really need someone who is familiar with transparency with how I can give my popup log in with a little transparency..nothing too much. Or a website that has instruction on how I can do this please?? If a css code is needed or how to do this?

GG2012, Please keep the Color to the default as it’s for staff members use only.

I would think you can't.

sorry.
MrMario can you help me with trasnparency for my table? the tutorials didn't work for my punbb.

What tutorials?

I saw somewhere here of someone had made a tutorial or instructions on how to give the log-in popup transparency a few months back, but I am unable to find it now. I don't know the css code for it.