Issue #3225972 by yovanny.gomez.oyola: After moving from Drupal 8.9 to 9.2.2,...

Issue #3225972 by yovanny.gomez.oyola: After moving from Drupal 8.9 to 9.2.2, the 'form-item' class disappeared from the details type fields

src/Plugin/better_exposed_filters/filter/FilterWidgetBase.php

@@ -215,6 +215,9 @@ abstract class FilterWidgetBase extends BetterExposedFiltersWidgetBase implement
         '#type' => 'details',
         '#title' => $exposed_label,
         '#description' => $exposed_description,
+        '#attributes' => [
+          'class' => ['form-item'],
+        ],
       ];
 
       if ($is_secondary) {