[libadwaita/wip/exalm/tab-style: 4/5] stylesheet: Add a backdrop style for tabs

[Alexander Mikhaylenko <alexm src gnome org>]

commit dfb812fb874096069bab1bf63c0f461ba36faec2
Author: Alexander Mikhaylenko <alexm gnome org>
Date:   Thu Apr 7 02:21:18 2022 +0400

    stylesheet: Add a backdrop style for tabs
    
    Now that we don't have borders touching the header bar border anymore, we
    can do this.

 src/stylesheet/widgets/_tab-view.scss | 6 ++++++
 1 file changed, 6 insertions(+)
---
diff --git a/src/stylesheet/widgets/_tab-view.scss b/src/stylesheet/widgets/_tab-view.scss
index 66649b12..2dff04d6 100644
--- a/src/stylesheet/widgets/_tab-view.scss
+++ b/src/stylesheet/widgets/_tab-view.scss
@@ -69,6 +69,12 @@ tabbar {
     &:backdrop .box {
       background-color: $headerbar_backdrop_color;
       transition: $backdrop_transition;
+
+      > scrolledwindow,
+      > .start-action,
+      > .end-action {
+        filter: opacity(0.5);
+      }
     }
   }
 }