Your #nav-bar should always be at the top of the viewport.
This was an annoying test for me as well. My #nav-bar was indeed at the top of the viewport, but it wouldn’t pass. The solution is to add position: fixed to your #nav-bar. Then of course you need to configure your top , right , bottom , and left properties, making sure top is set to 0.
Still, if you could share your code that would be helpful.
Nicolas