Adding background to Simple theme sidebar & body?

[starlightstitch]

I've added a background image to the Simple theme, but now I'd like to have solid-color backgrounds behind the sidebar menu and the main body of all pages (where products/collections/content would appear). I can't find the element that needs to be modified in the code, though, and I'm pulling my hair out. I've attached a screenshot with the two sections that I want to add backgrounds to. Can anybody tell me where in the code to add the background css?

Thanks!

[starlightstitch]

Edit: I managed to get a background on the sidebar by modifying .site-nav ul, yay! Still not sure what needs to be changed to get a background behind the main content.

[starlightstitch · Accepted solution]

Aaaand I found it. It was, conveniently enough, .main-content.

So I suppose I posted here just to give myself the impetus to figure it out on my own, haha.

[Salman111]

How do you change the background color of sidebar in simple theme?

[Puneet1301]

Do you have code to add the background image?

[CPSC]

How did you end up changing the background image in the Simple theme? I've been trying and can't seem to get the hang of it.