For 1, your navbar isn’t at the top, so it certainly isn’t always at the top. First you need to move it to the top of the page, and then you need to make sure it stays at the top, even when you scroll down. (Try looking into
position: fixed to use in the CSS for the navbar.) This is what they mean by the top of the viewport, no matter where you are on the page the navbar should still be visible at the top.
For 2, well, you aren’t using any media queries! These are used to style the same page differently depending on the size of the display it is being viewed with. See here for some more info and examples using them.