Main Menu Color Change

Main Menu Color Change

I am trying to target the header element of a drop down menu which I load
in jfiddle here: http://jsfiddle.net/DZLtm/16/
I am trying to get it so when you roll over nav ul li it show black
instead of red. Here are the lines that I would have thought would do it.
nav ul li {float: right; width: 172px; height: 35px; background-color: red;}
nav ul li:hover > ul {display: block; text-align: left; background-color:
black;}
Can someone please tell me why nav ul li:hover wont work and what is > ul
have to do with it. When I remove it it breaks the menu. Thank you Frank!