.thumbnail{
position: relative;
width:250px;
height:100px;
}

.thumbnail:hover{
background-color: transparent;
width:250px;
height:100px;
}

.thumbnail span{ /*CSS for enlarged image*/
width:400px;
height:420px;
left: -900px;
position:absolute;
visibility: hidden;
color: black;
text-decoration: none;
background:url(images/FD_prebio_backplate_299-320.jpg) no-repeat bottom right; 
}

.thumbnail:hover span{ /*CSS for enlarged image on hover*/
visibility: visible;
top: -200px;
left: 200px; /*position where enlarged image should offset horizontally */
}