Mobile burger menu – background color

Hi!

How can I change the mobile menu bg color?
I managed to change the top header color using the following code snippet as found in one of the solutions around the forums here:

div#header_main {
background-color: black;
}
div#header_main_alternate {
background-color: black;
}

I can’t, however, find how to change the color for the mobile menu. I tried a few different codes, but none of them worked – I probably used the wrong ones.
Could someone help out?

You can find the website here: https://ag-gardenanddriveways.co.uk/
(just swap between desktop and mobile layouts and look at the menu…)

That being said – how come the menu background color isn’t exposed in the settings anywhere? It’s such a basic feature, you shouldn’t need to fiddle with quick CSS to change it when the rest of the theme is so versatile…

Thanks!