update style of demo app

src/Shared/HandyControlDemo_Shared/UserControl/Main/PracticalDemo.xaml

@@ -0,0 +1,8 @@
+<UserControl x:Class="HandyControlDemo.UserControl.PracticalDemo"
+             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+             mc:Ignorable="d"
+             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
+             xmlns:d="http://schemas.microsoft.com/expression/blend/2008">
+    
+</UserControl>