td a span{display: none}
td a:hover span{ /*lo span verrý mostrato solo sullo stato :hover */
    display: block; 
    position:absolute;
    width: 180px;
    border: 1px solid #ffffff; 
    background-color: #003591; 
    padding:8px;
    font-size: 12px;
    text-align: center;
    color:#ffffff}