I am trying to customize the side menu

I want to let the user choose custom pre-made themes and this is causing an issue. I’m not sure what I should be targeting to apply SCSS rules to apply to the side menu. The main header is fine it is just the white area under the list of pages.

I’ve tried targeting .menu-inner, ,scroll-content and a myriad of other classes. I’ve tried to put in my own custom classes but nothing seems to work.

I can target most of the nav/header with .toolbar-background but hidden side menu doesn’t style.

Thanks for reading!