diff --git a/core/modules/system/src/Form/ThemeAdminForm.php b/core/modules/system/src/Form/ThemeAdminForm.php
index 9aa7123..27f8098 100644
--- a/core/modules/system/src/Form/ThemeAdminForm.php
+++ b/core/modules/system/src/Form/ThemeAdminForm.php
@@ -49,6 +49,7 @@ public function buildForm(array $form, FormStateInterface $form_state, array $th
     $form['admin_theme']['actions']['submit'] = array(
       '#type' => 'submit',
       '#value' => $this->t('Save configuration'),
+      '#button_type' => 'primary',
     );
     return $form;
   }