diff --git a/testsuite/reftests/separator-size.css b/testsuite/reftests/separator-size.css
index 2dff8740b1..1463c97083 100644
--- a/testsuite/reftests/separator-size.css
+++ b/testsuite/reftests/separator-size.css
@@ -1,3 +1,4 @@
+notebook,
 notebook stack {
   background: none;
 }