[gnome-shell-sass] theme: fix submenu separator contrast

[Florian Müllner <fmuellner src gnome org>]

commit 1e08c35df31a8221ac217621410c826c38158607
Author: Jakub Steiner <jimmac gmail com>
Date:   Thu Feb 13 21:45:02 2020 +0100

    theme: fix submenu separator contrast
    
    Fixes https://gitlab.gnome.org/GNOME/gnome-shell/issues/2203

 widgets/_popovers.scss | 5 +++++
 1 file changed, 5 insertions(+)
---
diff --git a/widgets/_popovers.scss b/widgets/_popovers.scss
index 5a741df..2dd2b53 100644
--- a/widgets/_popovers.scss
+++ b/widgets/_popovers.scss
@@ -86,6 +86,11 @@ $popover_arrow_height: 12px;
   height: 1px; //not really the whole box
   margin: 6px 64px;
   background-color: lighten($borders_color, 2%);
+  .popup-sub-menu & { //submenu separators
+    @if $variant == 'dark' {
+      background-color: lighten($bg_color,10%);
+    }
+  }
 }
 
 // desktop background menu