CSS & Headers, what am I missing?

I’d be so grateful if somebody could help me with a small CSS tweak – I just cannot find what I need to do.

My site is dinner-club.co.uk and I am trying to get rid of the white header so that the main image & content fills the full screen.

I can see that the element that contains the white space is 83px high but I cannot find the right element to adjust.

I’m sure it’s a tiny thing, if anybody can help that would be great.

Thanks a lot