感谢Ed Nailor&；库克鲁特！

http://ednailor.com/2011/01/24/adding-custom-css-classes-to-sidebar-widgets/

    // __________________________________________________________
//
// CUSTOM CLASS BY WIDGETS

function kc_widget_form_extend( $instance, $widget ) {
 if ( !isset($instance[\'classes\']) )
 $instance[\'classes\'] = null;
 /* Set your predetermied class choices here */
 $myarray = "class1,class2,class3";

$myclasses = explode(",",$myarray);
 $row = "
\\n";
 $row .= "\\tid_base}-{$widget->number}-classes\'>Class:\\n";
 $row .= "\\tid_base}[{$widget->number}][classes]\'  id=\'widget-{$widget->id_base}-{$widget->number}-classes\'  class=\'widefat\'>\\n";
 foreach($myclasses as $myclass) {
 $instance_selected = null; if($instance[\'classes\']==$myclass) $instance_selected = " selected=\'selected\'";
 $row .= "\\t".$myclass."\\n";
 }
 $row .= "\\n";
 echo $row;
 return $instance;
}
add_filter(\'widget_form_callback\', \'kc_widget_form_extend\', 10, 2);function kc_widget_update( $instance, $new_instance ) {
 $instance[\'classes\'] = $new_instance[\'classes\'];
 return $instance;
}
add_filter( \'widget_update_callback\', \'kc_widget_update\', 10, 2 );
function kc_dynamic_sidebar_params( $params ) {
 global $wp_registered_widgets;
 $widget_id    = $params[0][\'widget_id\'];
 $widget_obj    = $wp_registered_widgets[$widget_id];
 $widget_opt    = get_option($widget_obj[\'callback\'][0]->option_name);
 $widget_num    = $widget_obj[\'params\'][0][\'number\'];

 if ( isset($widget_opt[$widget_num][\'classes\']) && !empty($widget_opt[$widget_num][\'classes\']) )
 $params[0][\'before_widget\'] = preg_replace( \'/class="/\', "class=\\"{$widget_opt[$widget_num][\'classes\']} ", $params[0][\'before_widget\'], 1 );

 return $params;
}
add_filter( \'dynamic_sidebar_params\', \'kc_dynamic_sidebar_params\' );