You can't center a position:fixed element. The best you can do is center the parent container.
nav {
border: 1px solid red; //*for demo purposes only**/
width: 90%; /**adjust width as desired in px or %**/
margin: 1% auto 0 auto; //*this is centered**/
padding: 0;
}
If you want a responsive menu on mobile and tablets, look at jQuery Mean Menu. See example below:
Nancy O.