diff --git a/setup/styles.css b/setup/styles.css
index b123662208..9803a3a252 100644
--- a/setup/styles.css
+++ b/setup/styles.css
@@ -288,6 +288,10 @@ fieldset.optbox {
   padding: 0;
 }
 
+.setup-page fieldset.optbox {
+  width: 100%;
+}
+
 fieldset fieldset {
   margin: 0.8em;
   border: 1px solid #aaa;
diff --git a/templates/setup/base.twig b/templates/setup/base.twig
index 7fe7fb6ff5..754a2d3e27 100644
--- a/templates/setup/base.twig
+++ b/templates/setup/base.twig
@@ -40,7 +40,7 @@
   </ul>
 </div>
 
-<div id="page">
+<div id="page" class="setup-page">
   {% block content %}{% endblock %}
 </div>