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

table.tablesorter thead th span {
    margin-right: 1em;
}