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

.thumbnail:hover{
background-color: transparent;
z-index: 10;
}

.thumbnail span{ /*CSS for enlarged image*/
position: absolute;
background-color: #666666;
padding: 4px;
left: -1000px;
border: 1px solid #CCCCCC;
visibility: hidden;
color: #FFFFFF;
text-decoration: none;
}

.thumbnail span img{ /*CSS for enlarged image*/
border-width: 0;
border: 1px solid #CCCCCC;
}

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

}