You will need a different approach to center that. You don't center it now, all you do is space out 4 li's so it looks centered. When containing psholder narrows up to less than 4 li's, it looks differrent...until you get narrow enough that 3 li's fit and look centered.
Try it like this example instead
. Look closely in that example how the containing ul is
and the child li's are
You seem to be randomly naming div elements which is invalid. While <nav> is a valid element in HTML5, your DocType does not support that. Check your code in the validator and it will show you what I'm talking about.
Also, do you really need to nest that ul in 2 containing elements? I don't see <psel> doing much for you anyway.