[gtk/wip/exalm/polish: 2/8] adwaita: Make popover border transparent

[Alexander Mikhaylenko <alexm src gnome org>]

commit f47aba05b058454c23a8925dcd14cfec4d207498
Author: Alexander Mikhaylenko <alexm gnome org>
Date:   Thu May 7 00:19:03 2020 +0500

    adwaita: Make popover border transparent
    
    Port 379669b153595fd1a33b200f6b08e7d5ba0407f4 from GTK3.

 gtk/theme/Adwaita/_common.scss | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/gtk/theme/Adwaita/_common.scss b/gtk/theme/Adwaita/_common.scss
index 1c2a87c5fc..cacedb5045 100644
--- a/gtk/theme/Adwaita/_common.scss
+++ b/gtk/theme/Adwaita/_common.scss
@@ -1828,13 +1828,15 @@ popover.background {
 
   > arrow,
   > contents {
+    $_popover_border: if($variant=='light', transparentize(black, 0.77), transparentize($borders_color, 
0.1));
+
     background-color: $popover_bg_color;
-    border: 1px solid $borders_color;
+    background-clip: padding-box;
+    border: 1px solid $_popover_border;
     box-shadow: 0 1px 2px transparentize(black, 0.7);
 
     &:backdrop {
       background-color: $backdrop_bg_color;
-      border-color: $backdrop_borders_color;
       box-shadow: none;
     }
   }