<Window x:Class="CustomPanel.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:loc="clr-namespace:CustomPanel"
    SizeToContent="WidthAndHeight"
    Title="CustomPanel" Height="300" Width="300"
    >
  <loc:DiagonalPanel>
    <Button Content="Click me!" />
    <Rectangle Fill="Cyan" Stroke="Black"
               Width="100" Height="50" />
    <TextBlock Text="Hello, world!" />
    <Button Content="Click me too please" />
  </loc:DiagonalPanel>
</Window>
