nav ul ul {
	display: none;
}

	nav ul li:hover > ul {
		display: block;
	}
nav ul {
	background: #efefef; 
	background: linear-gradient(top, #efefef 0%, #5f6975 100%);  
	background: -moz-linear-gradient(top, #efefef 0%, #5f6975 100%); 
	background: -webkit-linear-gradient(top, #efefef 0%,#5f6975 100%); 
	box-shadow: 0px 0px 9px rgba(0,0,0,0.15);
	padding: 0 20px;
	border-radius: 10px;  
	list-style: none;
	position: relative;
	display: inline-table;
}
	nav ul:after {
		content: ""; clear: both; display: block;
	}
nav ul li {
	float: left;
}
	nav ul li:hover {
		background: #CCCCCC;
		background: linear-gradient(top, #5f6975 0%, #bbbbbb 40%);
		background: -moz-linear-gradient(top, #5f6975 0%, #bbbbbb 40%);
		background: -webkit-linear-gradient(top, #5f6975 0%,#bbbbbb 40%);
	}
		nav ul li:hover a {
			color: #fff;
		}
	
	nav ul li a {
		display: block; padding: 25px 40px;
		color: #222222; text-decoration: none;
	}
nav ul ul {
	background: #5f6975; border-radius: 0px; padding: 0;
	position: absolute; top: 100%;
}
	nav ul ul li {
		float: none; 
		border-top: 1px solid #6b727c;
		border-bottom: 1px solid #575f6a;
		position: relative;
	}
		nav ul ul li a {
			padding: 15px 40px;
			color: #fff;
		}	
			nav ul ul li a:hover {
				background: #4b545f;
			}
nav ul ul ul {
	position: absolute; left: 100%; top:0;
}
<style type="text/css">

.thumbnail{
position: relative;
z-index: 0;
}

.thumbnail:hover{
background-color: transparent;
z-index: 50;
}

.thumbnail span{ /*CSS for enlarged image*/
position: absolute;
background-color: black;
padding: 5px;
left: -500px;
border:0;
visibility: hidden;
color: black;
text-decoration: none;
}

.thumbnail span img{ /*CSS for enlarged image*/
border-width: 0;
padding: 2px;
}

.thumbnail:hover span{ /*CSS for enlarged image on hover*/
visibility: visible;
top: 1;
left: 50px; /*position where enlarged image should offset horizontally */

}

</style>
.background {
  background-color: black;
  opacity: 90%;
  filter:alpha(opacity=90);
  background-color: rgba(0,0,0,0.90);
  width: 100%;
  min-height: 100%;
  overflow: hidden;
  position: absolute;
  top: 0;
  left: 0;
  color: white;
}