No margin

   
      
<Window xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  Title="About WPF" 
  Background="OrangeRed">

    <Canvas>


      <Border BorderBrush="Black" BorderThickness="1">
        <Label Background="Aqua">0</Label>
      </Border>

    </Canvas>

</Window>