can't change menu backgrounds

I’ve tried to change the menu backgrounds at
lifeinthisplace.com
I was able to change a:hover color
but I was not able to change background colors for any menu-item
For example I added

#header #navbar ul li{
background-color:blue;
}

to style.php and got no change
It works when I change these in Firebug but not on the page when I change it in style.php or style.css