Can you make sure that the “Mobile Background Color” option for your “Navigation” is not set to the transparent value please?
You can easily change this theme option in the Customizer. Just go to your dashboard and navigate to “Appearance > Customize > Navigation”. Then, open the “Style” tab and check the “Mobile Background Color” value.
You're trying to setup your theme but you're experiencing errors when importing the demo content? Or you've just followed the setup guide but your website doesn't look exactly like our demo? These are common issues for which you can find easy and quick fixes.