fix z-index for drawer

src/client/styles/scss/_sidebar.scss

@@ -152,7 +152,7 @@
 
 // Drawer Mode
 @mixin drawer() {
-  z-index: $zindex-fixed + 1;
+  z-index: $zindex-fixed + 2;
 
   // override @atlaskit/navigation-next styles
   div[data-testid='Navigation'] {
@@ -230,5 +230,5 @@
 }
 
 .grw-sidebar-backdrop.modal-backdrop {
-  z-index: $zindex-fixed - 4;
+  z-index: $zindex-fixed + 1;
 }