New menu sidebar question

Is it possible to change the sidebar to black? I'm used to the old one, which had a black background, and as far as I can tell, you can't just change the new sidebar.

Isn't the default just black? Try setting your theme or something to black, maybe that would help

That changes the entire theme to dark, which basically just has the stuff on your background, not on a box.

That's the same as changing to dark mode.