.gallerycontainer{
position: relative;
margin-top:.5em;
/*Add a height attribute and set to largest image's height to prevent overlaying*/
}

a.thumbnail{
    position:relative; /*this is the key*/
    z-index:24; background-color:#fff;
    text-decoration:none;
	}

a.thumbnail:hover{z-index:25; background-color:#fff}

a.thumbnail span{
	display: none;
	}

a.thumbnail:hover span{ /*the span will display just on :hover state*/
    display:block;
    position:absolute;
    top:2em; left:7em; width:30em;
    border:10px solid #8eb832;
	padding-left:1em;
	padding-top:1em;
	padding-bottom:1em;
	padding-right:1em;
    background-color:#d7e6b6; color:#000;
	text-align: left
	}