The issue is because the Logo and Navigation simply could not fit in a certain range of screen sizes. Decreasing the logo and font size in the said range of screen sizes would require custom media queries. Regretfully, that would be outside the scope of our support because the theme does not offer that option.
You can further reduce the Logo size and also reduce the Navbar Top Link Spacing and maybe reduce the Font Size a bit.
Darshana suggested also that you try the Stacked Header Layout. That is the correct layout if the logo and navigation won't fit. If you wish to stay with Inline layout though, you will need to follow the suggestion I've just mentioned.
I see you're using Pro though so I'd recommend that you try out to build a custom header. You'll have more options. Please check out the Header and Footer Builder Introduction and the rest of the tutorials in our Knowledge Base.