It looks like you did it right, the only issue is that the menu text is showing up behind the background image. So adding z-index to the Nav should fix it.
Add this – z-index: 99; to the .nav-primary in your css. You can either edit the style.css directly (search for it in your css) or you can add it to your Custom CSS section in the Customiser page (recommended way) –
Once you add that it should show up in front of the background image. You’ll probably want to add in your CSS styles/adjustments to get it to appear however you want it to look.