table.tablesorter thead tr .header {
    background-image: url(../images/bg.gif);
    background-repeat: no-repeat;
    background-position: center right;
    cursor: pointer;
    height: 40px;
}

table.tablesorter thead tr .headerSortUp {
    background-image: url(../images/asc.gif);
}
table.tablesorter thead tr .headerSortDown {
    background-image: url(../images/desc.gif);
}
table th {
           cursor:pointer;
}
table thead th:hover { background-color:#dad8d8;}