[gtk/wip/jimmac/popover-separators] Adwaita: increase cotrast of popover separators

[Jakub Steiner <jimmac src gnome org>]

commit fa0a2af0472346c1a18e7163706dc0f80b012326
Author: Jakub Steiner <jimmac gmail com>
Date:   Mon Jan 4 17:53:40 2021 +0100

    Adwaita: increase cotrast of popover separators
    
    Fixes https://gitlab.gnome.org/GNOME/gtk/-/issues/3535

 gtk/theme/Adwaita/_common.scss | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
---
diff --git a/gtk/theme/Adwaita/_common.scss b/gtk/theme/Adwaita/_common.scss
index d64cc120da..c61c6a8f23 100644
--- a/gtk/theme/Adwaita/_common.scss
+++ b/gtk/theme/Adwaita/_common.scss
@@ -1831,7 +1831,10 @@ popover.background {
       background-color: transparent;
     }
 
-    separator { margin: 3px; }
+    separator {
+      background-color: mix($bg_color, $borders_color, 30%);
+      margin: 3px;
+    }
 
     list separator { margin: 0; }
   }