The whole setup is in the jsfiddle page here
The problem is that, the div block seems to conflict with the floating navigation bar so that the JavaScript dropdown does not work anymore.
This is a follow-up question of this old one:
How to make this navigation bar floating on top while scrolling?
You just need to add
z-indexto yournav, like so:Or, as an option, you can locate
<nav>below<div id="content">in html code.