diff --git a/core/modules/system/templates/indentation.html.twig b/core/modules/system/templates/indentation.html.twig
index e5e7b32..e07e3c1 100644
--- a/core/modules/system/templates/indentation.html.twig
+++ b/core/modules/system/templates/indentation.html.twig
@@ -17,4 +17,4 @@ See https://api.drupal.org/api/function/theme_indentation/8 for details.
 After copying this file to your theme's folder and customizing it, remove this
 HTML comment.
 -->
-{% for i in 1..size if size > 0 %}<div class="indentation">&nbsp;</div>{% endfor %}
+{% for i in 1..size if size > 0 %}<div class="js-indentation indentation">&nbsp;</div>{% endfor %}