[libadwaita/wip/jimmac/devel-headerbar-stripes] headerbar: stripy tint for devel windows

[Jakub Steiner <jimmac src gnome org>]

commit 02e3ba72e140add5150b5b492eafffc8ee523341
Author: Jakub Steiner <jimmac gmail com>
Date:   Tue Jul 20 14:29:33 2021 +0200

    headerbar: stripy tint for devel windows
    
    - better styling for devel apps (flat windows / no headerbar
      and split headerbars too)
    - Works better overall due to the visual link to devel icons.
    
    Fixes https://gitlab.gnome.org/GNOME/libadwaita/-/issues/232

 src/stylesheet/widgets/_header-bar.scss | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)
---
diff --git a/src/stylesheet/widgets/_header-bar.scss b/src/stylesheet/widgets/_header-bar.scss
index 4ff5990e..bf3f3d68 100644
--- a/src/stylesheet/widgets/_header-bar.scss
+++ b/src/stylesheet/widgets/_header-bar.scss
@@ -129,8 +129,25 @@ windowtitle {
 
 // Development versions of apps to use a differently styled headerbar
 
+@mixin devel-stripes($_fadeto) {
+  background:
+      linear-gradient(to bottom, transparent, $_fadeto),
+      repeating-linear-gradient(
+        45deg,
+        transparentize($fg_color, .955),
+        transparentize($fg_color, .955) 10px,
+        transparent 10px,
+        transparent 20px
+      );
+}
+
 window.devel {
   headerbar > windowhandle {
-    background: cross-fade(8% -gtk-icontheme("system-run-symbolic"), image(transparent)) 90% 0/256px 256px 
no-repeat;
+    @include devel-stripes($headerbar_bg_color);
+
+    &:backdrop { background: image(transparent); }
+  }
+  headerbar.flat > windowhandle {
+    @include devel-stripes($bg_color);
   }
 }