title: Style field modification from .cs code
body: <p>I have a style described in Grid.resources. How could I modify height and width(in my sample they are 20 and 20) of Ellipse from Thumb? Other properties are accessible from other parts of code but not this((</p>
  
  <pre><code>&lt;Style x:Key="CustomThumbForSlider" TargetType="{x:Type Thumb}"&gt;
      &lt;Setter Property="OverridesDefaultStyle" Value="True"/&gt;
      &lt;Setter Property="Template"&gt;
          &lt;Setter.Value&gt;
              &lt;ControlTemplate TargetType="{x:Type Thumb}"&gt;
                  &lt;Ellipse Fill="Transparent" Stroke="#FF000000" StrokeThickness="3" Height="20" Width="20"/&gt;
              &lt;/ControlTemplate&gt;
          &lt;/Setter.Value&gt;
      &lt;/Setter&gt;
  &lt;/Style&gt;
  </code></pre>