Reducing header height?

[dhae_knight_1]

I'm using Underworld for Crossroads, and the header is cooking my noodle. I would love to reduce the height of the header to... pretty much what's needed for the navigational elements, now I've figured out how to insert an image as title. I've checked the page source, but... either it's been way too long since I worked with CSS last, or the header elements are on an external style-sheet somewhere.

Can I do this at all, or do I need to make my very own style from scratch?

Also... I think I might like to move the navigation module to the left down just a smidgen. Anybody got pointers to that effect?