add z-index

packages/app/src/styles/_navbar.scss

@@ -1,6 +1,7 @@
 .grw-navbar {
   top: -$grw-navbar-height !important;
 
+  z-index: 1035 !important; // should be higher than SubNavigation
   max-height: $grw-navbar-height + $grw-navbar-border-width;
   border-top: 0;
   border-right: 0;