Thanks to the support knowledge based at optimizepress.com I was able to center the navigation menu for each of the pages that I was working on by adding the following line of code into the other scripts section of the page:
body .container .navigation ul { text-align: center; }
body .container .navigation ul li { float: none; display: inline-block; }
.page-header .navigation ul li { display: inline-block; }
You will have to go to the page and then here:
Use this custom css by adding it to Page Settings > Other Scripts > Custom CSS (select from dropdown):
