Customzed header…but displays weird on Macs

There are actually subtle differences between the exact same browser version on different operating systems.

It should be as simple as bringing the menu font size down just a little bit in this case:

nav #site-nav li a {
  font-size: 18px;
}

There are some tools that can assist in testing the wide variety of variables which one is not likely to have total access to the real thing for.

Mobile Testing – https://quirktools.com/screenfly/

Browser Testing – https://browsershots.org/