RadialGradientBrush SpreadMethod=Pad

   
  


<Window x:Class="Workspace.DockExample"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Workspace" Width="640" Height="480">

    <Canvas Grid.Row="4" Grid.Column="4" Width="150" Height="75" Margin="0,0,0,10">
      <Rectangle Width="150" Height="75" Stroke="Black">
        <Rectangle.Fill>

          <RadialGradientBrush Center="0.5,0.5" RadiusX="0.3" RadiusY="0.3" SpreadMethod="Pad">
            <GradientStop Color="White" Offset="0" />
            <GradientStop Color="#333333" Offset="1" />
          </RadialGradientBrush>
        </Rectangle.Fill>
      </Rectangle>
      <Line X1="75" Y1="15" X2="75" Y2="60" />
      <Line X1="30" Y1="37.5" X2="120" Y2="37.5" />
    </Canvas>

</Window>