Vantage: Changing Design of the Responsive Menu

Hi Folks,

i am a proud User of the Vantage Theme and after working with it over 2 years, there is one question i cannot solve:

How can I change the Colours and the Fonts of the Responsive Menu (which only appears on smalls Screens like Mobiles)?
I’ve been looking in the *.css and the other Files – even hunting for the Colour Codes (grey) wasn’t successful.

Best Regards from Thomas