title: Make the header column separator visible
body: <p>I have used this xaml code to modify the background color of my DataGrid Header and the column separator visibility. My problem is that the column separators are elminated so the column headers look a little bit different:</p>
  
  <p>this is my code :</p>
  
  <pre><code>&lt;DataGrid AutoGenerateColumns="False" Grid.ColumnSpan="9" Grid.Row="1" Height="82" HorizontalAlignment="Left" Margin="99,427,0,0" Name="dataGrid1" VerticalAlignment="Top" Width="363" Background="#9DB9EB" &gt;
      &lt;DataGrid.Columns&gt;
          &lt;DataGridTextColumn Header="Header1" /&gt;
          &lt;DataGridTextColumn Header="Header2" /&gt;
      &lt;/DataGrid.Columns&gt;
      &lt;DataGrid.ColumnHeaderStyle&gt;
          &lt;Style TargetType="{x:Type DataGridColumnHeader}"&gt;
              &lt;Setter Property="Background" Value="#cee8ef" /&gt;
              &lt;Setter Property="BorderThickness" Value="2" /&gt;
          &lt;/Style&gt;
      &lt;/DataGrid.ColumnHeaderStyle&gt;
  &lt;/DataGrid&gt;
  </code></pre>
  
  <p>How can I make the header column separtor visible?</p>