How do I make my Navbar responsive for Tribute Page?

I am currently working on the Responsive Web Design Project- Tribute Page. I am trying to make my Nav Bar responsive, but I am not sure how to keep it fixed and in the middle of the page. When I reduce the width of the page the navbar shifts to the left.

Here is the link to my codepen.

I have tried googling but I am still struggling. Any help will be appreciated.

Try this:

header {
  position: sticky;
  position: -webkit-sticky;
  top: 0; /* required */

  display: flex;
  justify-content: center;
  width: 100%;