Add a select box to all widgets

Thanks to Ed Nailor & Kucrut !

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']) )
 $params[0]['before_widget'] = preg_replace( '/class="https://wordpress.stackexchange.com/", "class=\"{$widget_opt[$widget_num]['classes']} ", $params[0]['before_widget'], 1 );

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