Hm, well it depends on how you want to fix it.
1) Make the header non-sticky for smaller displays
2) Make the logo and search smaller and decrease the amount of links so that it fits between
3) Make the header menu links less, and use a More link dropdown as last menu item for all links that doesn’t fit on small screens
I’d pick #3, as you can see here on the demo it works fine on smaller displays:
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