[gtk/wip/baedert/for-master] adwaita: Reset popover background in backdrop

[Timm Bäder <baedert src gnome org>]

commit b37b85333df88f90a3cb8bd7f7a12680cd42ce15
Author: Timm Bäder <mail baedert org>
Date:   Sat Aug 1 10:31:53 2020 +0200

    adwaita: Reset popover background in backdrop
    
    Otherwise it inherits the generic background color from .background
    
    Fixes #2766

 gtk/theme/Adwaita/_common.scss | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/gtk/theme/Adwaita/_common.scss b/gtk/theme/Adwaita/_common.scss
index 104f09d707..a2f4eab20b 100644
--- a/gtk/theme/Adwaita/_common.scss
+++ b/gtk/theme/Adwaita/_common.scss
@@ -1738,6 +1738,10 @@ popover.background {
     box-shadow: 0 1px 2px transparentize(black, 0.7);
   }
 
+  &:backdrop {
+    background-color: transparent;
+  }
+
   > contents {
     padding: 8px;
     border-radius: $popover_radius;