I would like to reduce the height of my main menu/header.  For example, I would like it to be 60px tall on a full size screen.

I would also like the sticky main menu to be the same size as the normal main menu. (i.e. when you scroll down, the main menu stays at the top but does not need to shrink.)

I am relatively proficient at css and editing child themes, so you can give me answers on that level if necessary.

Thanks!