How to customize mobile menu background color

I am trying to identify the proper class or menu hierarchy in order to modify the background color on the mobile responsive menus.

The default white color works acceptably on my desktop interface but on mobile devices it is difficult to distinguish the white menu from the white background page contents. I’m comfortable adding additional css through the customize theme option but have been unable to isolate the class(es) to change the menu bar for mobile only.

I’d like to change from white #ffffff to #78a3a5. TIA for your help
-=Rich=-