table.tablesorter th.tablesorter-headerUnSorted {
    background-image: url('bg.gif');
    background-repeat: no-repeat;
    background-position: center right;
    cursor: pointer;
}
table.tablesorter th.tablesorter-headerAsc {
    background-image: url('asc.gif');
    background-repeat: no-repeat;
    background-position: center right;
}
table.tablesorter th.tablesorter-headerDesc {
    background-image: url('desc.gif');
    background-repeat: no-repeat;
    background-position: center right;
}
table.tablesorter thead tr .tablesorter-headerDesc, .tablesorter-headerAsc {
background-color: #8dbdd8;
}