a.tooltip_link {
    position: relative; /*this is the key*/
    z-index: 24;
}

a.tooltip_link:hover {
	z-index:25;
}

a.tooltip_link span {
	display: none;
}

a.tooltip_link:hover span { /*the span will display just on :hover state*/
    display: block;
    position: absolute;
    top:20px;
	left: 15px;
    border: 1px dashed #000;
	padding: 4px;
    background-color:#fff;
	color:#000;
}