.gallerycontainer{
position: relative;
height: 500px;
/*Add a height attribute and set to largest image's height to prevent overlaying*/
}

a.thumbnail {
   text-decoration: none;
}

.thumbnail img{
   border: 0px solid;
   margin: 0 0 0 0;
   width: 56px;
   height: 38px;
}

.thumbnail:hover{
   background-color: transparent;
text-decoration: none;
}

.thumbnail:hover img{
text-decoration: none;
}

.thumbnail span{ /*CSS for enlarged image*/
   position: absolute;
   padding: 0;
   left: -1000px;
   border: 0;
   visibility: hidden;
   color: black;
}

.thumbnail span img{ /*CSS for enlarged image*/
   border-width: 0;
   padding: 0px;
   width: 500px;
   height: 298px;
}

.thumbnail:hover span{ /*CSS for enlarged image*/
   visibility: visible;
   top: 0px;
   left: 0px; 
  
}