Separate prefix styles from non-item styles in menus

Change-Id: I98255ac8a2e173c1d1c3fef3806fa490526b54cb
diff --git a/dev/js/src/menu/prefix.js b/dev/js/src/menu/prefix.js
index 3930e45..f6c6c76 100644
--- a/dev/js/src/menu/prefix.js
+++ b/dev/js/src/menu/prefix.js
@@ -18,6 +18,7 @@
 
     // Add prefix span
     t._el = document.createElement('span');
+    t._el.classList.add('non-item');
     t._el.classList.add('pref');
     // Connect action