Thank you for your response! Yes, I use Inspect Element frequently to see which classes to target for customizations.
The issue has to specifically do with the way the Twenty Nineteen theme truncates the main menu on mobile. When I target the classes to float left/right, the menu thinks it needs to kick itself into the mobile version. So maybe the classes are correct and there’s an extra creative step to tell the menu to stop truncating on desktop after the float somehow? From what I’ve seen online, it seems like other people are having the same issue but I haven’t seen anyone who’s resolved it yet. Any thoughts would be appreciated!