.gallerycontainer{
position: relative;
/*Add a height attribute and set to largest image's height to prevent overlaying*/
position: absolute; top: 0px; bottom: -1px; visibility: hidden;
}
.thumbnail{
position: relative;
z-index: 0;
}

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

.thumbnail span{ /*CSS for enlarged image*/
position: absolute;
background-color:#FFFFFF;
padding: 0px;
left: -1000px;
border: 1px dashed gray;
visibility: hidden;
color: black;
text-decoration: none;
}

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

.thumbnail:hover span{ /*CSS for enlarged image on hover*/
visibility: visible;
top: 40px;
left: 100px; /*position where enlarged image should offset horizontally */

}