[gnome-builder] css: soften headerbar background on Adwaita

[Christian Hergert <chergert src gnome org>]

commit f5c06c389c63a96e62832f9c4102f441dc73ea5d
Author: Christian Hergert <chergert redhat com>
Date:   Sat Jun 16 16:22:27 2018 -0700

    css: soften headerbar background on Adwaita
    
    We have lots of widgets near the headerbar border and it looks really
    chunky. I had hoped to delay this until an Adwaita revamp, but I'm not
    going to delay for that any longer.
    
    I don't think we need to do this for preferences, but we'll see.

 data/themes/Adwaita-shared.css | 8 ++++++++
 1 file changed, 8 insertions(+)
---
diff --git a/data/themes/Adwaita-shared.css b/data/themes/Adwaita-shared.css
index 257da25e4..1057b6412 100644
--- a/data/themes/Adwaita-shared.css
+++ b/data/themes/Adwaita-shared.css
@@ -1,5 +1,13 @@
 @import url("resource:///org/gnome/builder/themes/shared.css");
 
+/* soften the headerbar a bit which looks too chunky give the widget density
+ * near the bottom border.
+ */
+window.workbench headerbar {
+  border-bottom: 1px solid @borders;
+  background-image: none;
+}
+
 idelayoutstackheader > button:last-child {
   margin-right: 3px;
 }