I just looked at your site, everything seems to be working fine at a width of 1200px that you set. The nav sticks and the box-shadow displays as expected,
The one thing you need to do is increase
.p-sectionLinks-inner
's width from 1200px to 1204px so that it matches the width of the navigation tabs bar above it.
What is not working for you?
Edit: add this to
.p-nav
:
background-position: center;
, it makes your nav bar background look a lot better, in my opinion,