Omega Navigation not completely responsive

I use Omega theme in combination with Family child theme. Very beautiful because of ‘simplicity’, however….
The top navigation disappears at a certain moment and is not visible on smartphone screens.
I changed in css “tiny nav: display: none” into “display: inline” and indeed then I get a visible navigation on smartphone size. But this black navigation box is then also visible on the bigger screens under the normal visible navigation.

I couldn’t find a solution either to change the rather big black navigation box with white font(tiny nav) into a white (black bordered)box with black/grey font.
Anyway, till now showing tiny nav isn’t the solution, because on bigger screens 2 types of the same navigation appear then under each other.
Can you tell me how I can solve it in a way I keep everywhere just 1 top navigation in all screen sizes?
Thanks