table.tablesorter thead tr .headerSortUp {
    background-image: url(/img/tablesorter/asc.gif);
}
table.tablesorter thead tr .headerSortDown {
    background-image: url(/img/tablesorter/desc.gif);
}
table.tablesorter thead tr .header {
    background-image: url(/img/tablesorter/bg.gif);
    background-repeat: no-repeat;
    background-position: center right;
    cursor: pointer;
}