Drop-down background color and format

Hi there,

Im pretty new to wordpress and decided to use the customizr theme with nimble builder, but there are two things Id really love to change.

The background color of the drop down menu

The fact that in mobile and tablet view the top-menu turns into a hamburger menu.

Help with either of thes problems would be much appreciated. It stands between me and making a website I would like to provide to my client.

I know how to code to some extent. But I cannot find the css for the drop-down menu. It seems to be managed internally..

Anyways, thanks for your help in advance

The page I need help with: [log in to see the link]