I'm currently customizing my NodeBB forum using a custom theme, and I've run into a bit of a roadblock with the CSS. I've successfully made several changes, but I'm facing a challenge with one particular aspect.

I'm trying to style the user profile pop-up that appears when you click on a user's avatar or name. Specifically, I'd like to adjust the background color and font size for the information displayed in the pop-up.

I've tried adding custom CSS to the Custom Styles section in the ACP (Admin Control Panel) under Appearance > Custom CSS, but it doesn't seem to affect this particular pop-up. I've also tried inspecting the elements using browser developer tools, but I'm not sure which classes or IDs I should be targeting for this customization.

Could someone provide guidance on how to effectively target and style the user profile pop-up in NodeBB?