a.tooltip {
    position:relative; /*this is the key*/
    z-index:24; 
    text-decoration:underline}

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

a.tooltip span{display: none}

a.tooltip:hover span{ /*the span will display just on :hover state*/
    display:block;
    position:absolute;
    padding:3px;
    top:2em; left:2em; width:15em;
    border:1px solid #cccccc;
    background-color:#E0EAF4; color:#333333;
    text-align:left;
    text-decoration:none;}