Menu background color Desktop- vs. mobile-version

I’d like to make the background of the desktop menu transparent; the menu items will then have a light grey background with 90% opacity. If I change the background colour, this also applies to mobile devices with the hamburger menu. Unfortunately, this makes the hamburger menu difficult to read.

Can I set the background colour for the mobile version independently of the desktop version?
I don’t want to maintain two different menus, just different background colours.

One way to do this is to add a background box behind the mobile menu. This box can be set to not be visible on the desktop version.