Elgg logo and css

Hi, I am new around here as well but getting on with it best i can. Like what I see so far.

Want to know how to change the Elgg blue logo. I changed the code in the footer to a text link credit but amazingly the logo persists and the logo isn't in the graphics folder - so i've no idea where thats coming from.

In fact some aspect of changing the css arn't as straight forward as I am used to.  Like changing the dull grey background. Is there a guide to where the relative items are the css file.

I have searched on here and seen a couple of posts about header navigation bars. I can't find any plug ins for them so I guess it is a bit of hand coding time. I'd be happy with the default nav with a few changes. Can some one please point me to the right place in the files to customise the standard header.

Cheers