title: In WPF Style, How can Trigger access a son Element of the Element it is attatched
body: <p>The following is a Simple Style for ListBoxItem, ListBoxItem has a son Border. Border has a Padding property with value of 8, I want to change the value to 0, when the item is selected. How can I write the trigger?</p>
  
  <pre><code>    &lt;??Style TargetType="{x:Type ListBoxItem}"&gt;
          &lt;Setter Property="Background" Value="Transparent" /&gt;
          &lt;Setter Property="Template"&gt;
              &lt;Setter.Value&gt;
                  &lt;ControlTemplate TargetType="{x:Type ListBoxItem}" &gt;
                      &lt;Border 
                          SnapsToDevicePixels="True" 
                          HorizontalAlignment="Center" 
                          VerticalAlignment="Center"
                          Padding = "8"
                          Background="{TemplateBinding Background}"&gt;
                          &lt;ContentPresenter /&gt;
                      &lt;/Border&gt;
                      &lt;ControlTemplate.Triggers&gt;
                          &lt;Trigger Property="IsSelected" Value="True"&gt;
                              ??&lt;Setter Property="Padding" Value="0" /&gt;??   &lt;----How Can I do this?
                          &lt;/Trigger&gt;
                      &lt;/ControlTemplate.Triggers&gt;
                  &lt;/ControlTemplate&gt;
              &lt;/Setter.Value&gt;
          &lt;/Setter&gt;
      &lt;??/Style&gt;
  </code></pre>