a.tooltip{
    position:relative; /*this is the key*/
    z-index:0; background-color:#ffffff;
    color:#000;
    text-decoration:none}

a.tooltip:hover{z-index:25; background-color:#ffffff}

a.tooltip span{display: none}

a.tooltip:hover span{ /*the span will display just on :hover state*/
    display:block;
    position:absolute;
    top:1em; left:0em; width:18em;
    border:1px solid #003366;
    padding:4px;
    background-color:#ccffff; color:#000000;
    text-align: left}