reftests: Make separator-size test pass in HighContrastInverse

After neutralizing the stack background, the notebook itself
was peeking through.

diff --git a/testsuite/reftests/separator-size.css b/testsuite/reftests/separator-size.css
index 2dff8740b1af7c07bdfa6e09ce0a85a54ae8c592..1463c97083fbae7fe48b0aa724991bf2abb40b0b 100644 (file)
--- a/testsuite/reftests/separator-size.css
+++ b/testsuite/reftests/separator-size.css
@@ -1,3 +1,4 @@
+notebook,
 notebook stack {
   background: none;
 }