diff --git a/tests/reftests/background-size.css b/tests/reftests/background-size.css
index 5dbff99984..aae6f9f350 100644
--- a/tests/reftests/background-size.css
+++ b/tests/reftests/background-size.css
@@ -1,6 +1,6 @@
 @import "reset-to-defaults.css";
 
-* {
+.button {
   background-image: url("border-image-balls.png");
   color: black;
   text-shadow: 1px 1px white;