Fix IEF-ID breaks, leading to hard to debug errors

Closes #3417664

src/Plugin/Field/FieldWidget/InlineEntityFormBase.php

@@ -2,6 +2,7 @@
 
 namespace Drupal\inline_entity_form\Plugin\Field\FieldWidget;
 
+use Drupal\Component\Utility\Html;
 use Drupal\Core\Entity\EntityDisplayRepositoryInterface;
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\EntityTypeBundleInfoInterface;
@@ -168,6 +169,7 @@ abstract class InlineEntityFormBase extends WidgetBase implements ContainerFacto
   protected function makeIefId(array $parents) {
     $iefId = implode('-', $parents);
     $iefId = preg_replace('#-inline_entity_form-entities-([0-9]+)-form-#', '-$1-', $iefId);
+    $iefId = Html::cleanCssIdentifier($iefId);
     return $iefId;
   }