Added missing closing div tag.

Closes #3479988

src/Service/BlockClassHelperService.php

@@ -816,9 +816,11 @@ class BlockClassHelperService {
         $help_text = $this->t('Customize the this block by adding attributes. E.g. "data-block-type"="admin"');
 
         // Update the help text with the Modal to show this for the user.
-        $help_text .= ' - <div class="show-items-used">' . $this->t('<a href="@url_used_attribute_list@" class="use-ajax" data-dialog-options="{&quot;width&quot;:800}" data-dialog-type="modal">See all the attributes used</a>.', [
+        $help_text .= ' - <div class="show-items-used">';
+        $help_text .= $this->t('<a href="@url_used_attribute_list@" class="use-ajax" data-dialog-options="{&quot;width&quot;:800}" data-dialog-type="modal">See all the attributes used</a>.', [
           '@url_used_attribute_list@' => $url_used_attribute_list,
         ]);
+        $help_text .= '</div>';
 
         // Create the field group for multiple attributes.
         $form['multiple_attributes']['third_party_settings']['block_class']['attribute_' . $index] = [