File: htdocs/modules/system/themes/default/css/tablesorter.css

/*
 * Default Admin Theme
 *
 * @copyright       (c) 2000-2015 XOOPS Project (www.xoops.org)
 * @license         http://www.fsf.org/copyleft/gpl.html GNU public license 3.0
 * @package         themes
 * @since           2.5.x
 * @author          Xoops Design Theme <http://www.xoops.org/>
 * @maintained      Xoops Design Theme <http://www.xoops.org/>
 *
*/
table.tablesorter thead tr .header {
    background: url(../img/unsort.gif) no-repeat center right;
}

table.tablesorter thead tr .headerSortUp {
    background: url(../img/asc.gif) no-repeat center right;
}

table.tablesorter thead tr .headerSortDown {
    background: url(../img/desc.gif) no-repeat center right;
}