[gtk/gtk-3-24] Adwaita: backport nightly styling

[Jakub Steiner <jimmac src gnome org>]

commit 955aa8d54b1ef6b9252e06b19d1d42a971c2b409
Author: Jakub Steiner <jimmac gmail com>
Date:   Wed Oct 10 09:38:50 2018 +0200

    Adwaita: backport nightly styling
    
    - nightly apps get a headerbar styling

 gtk/theme/Adwaita/_common.scss | 11 +++++++++++
 1 file changed, 11 insertions(+)
---
diff --git a/gtk/theme/Adwaita/_common.scss b/gtk/theme/Adwaita/_common.scss
index 2d45f28a94..cfd272c918 100644
--- a/gtk/theme/Adwaita/_common.scss
+++ b/gtk/theme/Adwaita/_common.scss
@@ -1770,6 +1770,17 @@ headerbar { // headerbar border rounding
   @extend %titlebar;
 }
 
+// Development versions of apps to use a differently styled headerbar
+
+window.devel {
+  headerbar:last-child {
+    background: transparent -gtk-icontheme("system-run-symbolic") 90% 0/256px 256px no-repeat,
+                linear-gradient(to left, mix($selected_bg_color, $bg_color, 10%) 8%, $bg_color 25%);
+    color: transparentize($fg_color,.9);
+
+    label { color: $fg_color; }
+  }
+}
 
 /************
  * Pathbars *