[libadwaita/wip/exalm/background-colors2: 5/18] demo: Add .background to the flap sidebar

[Alexander Mikhaylenko <alexm src gnome org>]

commit 4384b9af8376882a488835a0c742269cd2c0545d
Author: Alexander Mikhaylenko <alexm gnome org>
Date:   Thu Sep 30 16:44:02 2021 +0500

    demo: Add .background to the flap sidebar
    
    We'll remove background from sidebars, adapt to that.

 examples/adw-flap-demo-window.ui | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/examples/adw-flap-demo-window.ui b/examples/adw-flap-demo-window.ui
index 720cb766..90dfcfe2 100644
--- a/examples/adw-flap-demo-window.ui
+++ b/examples/adw-flap-demo-window.ui
@@ -38,6 +38,9 @@
               <object class="GtkStackSidebar">
                 <property name="stack">stack</property>
                 <property name="width-request">200</property>
+                <style>
+                  <class name="background"/>
+                </style>
               </object>
             </property>
             <property name="separator">