thanks, that certainly helps to at least center the text of the nav. But the question remains as how to center the whole navigation menu, in a way that it keeps centered on different platforms (computer, pad, mobile).
Alex his solution of moving the navigation bar to the left 15% works for a computer screen, but on smaller screens (i.e. pad or mobile) it is pushed to the side. Is there a way to center the whole div in header.php, and would this work across different platforms?