public function updateEditForm($form) {
        $classNameField = $form->Fields()->dataFieldByName('ClassName');
        if ($classNameField) {
            $className = $classNameField->Value();
            if ($className === 'Site') 
            {
            	$form->Fields()->removeByName(array(SilverStripeNavigator::class));
                $form->removeExtraClass('cms-previewable');
            }
        }
    }