add a custom class for a wordpress widget

class name widget

/**
 * add class to widget
 *
 * 
 */

function kc_widget_form_extend( $instance, $widget ) {
  if ( !isset($instance['classes']) )
		$instance['classes'] = null;

		$row .= "Class:\t<input type='text' name='widget-{$widget->id_base}[{$widget->number}][classes]' id='widget-{$widget->id_base}-{$widget->number}-classes' class='widefat' value='{$instance['classes']}'/>\n";
		$row .= "</p>\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' );