menu bar color

Hey there, I would like to change the color of the menu bar. In the customizer I can only choose between my current dark grey, pink and a third option. I tried the classes main-navigation and nav-primary but It won't work. What can I do? Link: https://spielfrei.at Also, how can I change the length of the background color of the .site-description? I would like to be it as long as the text is. Thank you very much and greetings from Austria!