Reduce NavBar height in BP-Business Theme

I want to reduce the navbar's height in BP-Business Theme from 50px to 30px.

I changed the height of #top-navigation, in layout.css, and the height of navigation_background.png. It works, but the selected tab remains with the original height.

My guess it that I may be missing any padding...

Could you please help me?
Thanks & regards,
Edgard