Gap between menu and header

Hi there.

Im a newbie. Have created a child and updated my version of wordpress and now my menu bar is not connected to my header. there is a 50-100 pixel white gap between.

Have went through entire css and removed all padding pixels to 0 and followed all the other threads on this topic. Including reducing the size of header and playing around with the pixel parameters on css- which only led to entire page changing length.

I change the original twenty ten css in each case, as on my child the editor only shows the link to twenty ten css.

I am probably being dumb and not changing childs css directly may be the cause??

I would really appreciate any help with this problem

Cheers