reftests: Add missing css file for grid-expand test

diff --git a/tests/reftests/grid-expand.css b/tests/reftests/grid-expand.css
new file mode 100644 (file)
index 0000000..3549d52
--- /dev/null
+++ b/tests/reftests/grid-expand.css
@@ -0,0 +1,3 @@
+GtkEventBox {
+  background-color: green
+}