It would be great that you share with us your code for that we can check it to understand the issue. With what you are showing, it means that your navbar is not all the time visible on the viewport (your page), when you are scrolling down/top. The navbar should always be visible according to the user story of that project, no matter where you are on your page.
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Posting a small snippet of your code does not provide enough information for anyone to help you.
When you submit your project you have to provide a link to your live code. Show us that link so we can give you help without having to guess.
If you don’t want to do that then all we can say is when a test fails click the red button to see which test(s) are failing and text to help you correct the issue.
Be sure and read more than just the first line of the failing message. The ability to read and comprehend error messages is a skill you’ll need to acquire as a developer. Ask questions on what you don’t understand.
But again, we will need to see all of your code to provide help.
As said we need to see the full code, the HTML tells us absolutely nothing about the CSS.
If I had to guess you might be missing
top: 0 if it’s a positioned fixed nav. Or you might have some default margins pushing the content down.