[gtk: 4/5] gtk-demo: Avoid double borders in the blendmodes demo

[Matthias Clasen <matthiasc src gnome org>]

commit 09fa3886ba07813b34fb66a16e76c82402a4d473
Author: nana-4 <hnmaigo gmail com>
Date:   Fri Aug 7 00:54:46 2020 +0900

    gtk-demo: Avoid double borders in the blendmodes demo

 demos/gtk-demo/blendmodes.ui | 4 ++++
 1 file changed, 4 insertions(+)
---
diff --git a/demos/gtk-demo/blendmodes.ui b/demos/gtk-demo/blendmodes.ui
index e87a0a8970..5826f41d44 100644
--- a/demos/gtk-demo/blendmodes.ui
+++ b/demos/gtk-demo/blendmodes.ui
@@ -8,6 +8,10 @@
     <property name="default-height">300</property>
     <child>
       <object class="GtkGrid">
+        <property name="margin-start">12</property>
+        <property name="margin-end">12</property>
+        <property name="margin-top">12</property>
+        <property name="margin-bottom">12</property>
         <property name="row-spacing">12</property>
         <property name="column-spacing">12</property>
         <child>