title: How to animate Opacity of a DropShadowEffect?
body: <p>I have a WPF project with a border using the following style.  The plan is to get the glow effect to fade in when the mouse moves over the border, and fade out when it leaves.</p>
  
  <pre><code>&lt;Style x:Key="BorderGlow" TargetType="Border"&gt;
      &lt;Style.Resources&gt;
          &lt;Storyboard x:Key="GlowOn"&gt;
              &lt;DoubleAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetProperty="(DropShadowEffect.Opacity)"&gt;
                  &lt;SplineDoubleKeyFrame KeyTime="0:0:0.3" Value="1"/&gt;
              &lt;/DoubleAnimationUsingKeyFrames&gt;
          &lt;/Storyboard&gt;
          &lt;Storyboard x:Key="GlowOff"&gt;
              &lt;DoubleAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetProperty="(DropShadowEffect.Opacity)"&gt;
                  &lt;SplineDoubleKeyFrame KeyTime="0:0:0.3" Value="0"/&gt;
              &lt;/DoubleAnimationUsingKeyFrames&gt;
          &lt;/Storyboard&gt;
      &lt;/Style.Resources&gt;
  
      &lt;Setter Property="CornerRadius" Value="6,1,6,1" /&gt;
      &lt;Setter Property="BorderBrush" Value="{StaticResource SelectedBorder}" /&gt;
      &lt;Setter Property="BorderThickness" Value="1" /&gt;
      &lt;Setter Property="Background" Value="{StaticResource DeselectedBackground}" /&gt;
      &lt;Setter Property="RenderTransformOrigin" Value="0.5,0.5" /&gt;
      &lt;Setter Property="TextBlock.Foreground" Value="{StaticResource SelectedForeground}" /&gt;
  
      &lt;Setter Property="RenderTransform"&gt;
          &lt;Setter.Value&gt;
              &lt;RotateTransform Angle="90"/&gt;
          &lt;/Setter.Value&gt;
      &lt;/Setter&gt;
  
      &lt;Setter Property="Effect"&gt;
          &lt;Setter.Value&gt;
              &lt;DropShadowEffect ShadowDepth="0" BlurRadius="8" Color="#FFB0E9EF"/&gt;
          &lt;/Setter.Value&gt;
      &lt;/Setter&gt;
  
      &lt;Style.Triggers&gt;
          &lt;Trigger Property="IsMouseOver" Value="True"&gt;
  
              &lt;Trigger.EnterActions&gt;
                  &lt;BeginStoryboard Storyboard="{StaticResource GlowOn}"/&gt;
              &lt;/Trigger.EnterActions&gt;
  
              &lt;Trigger.ExitActions&gt;
                  &lt;BeginStoryboard Storyboard="{StaticResource GlowOff}"/&gt;
              &lt;/Trigger.ExitActions&gt;
  
          &lt;/Trigger&gt;
      &lt;/Style.Triggers&gt;
  &lt;/Style&gt;
  </code></pre>
  
  <p>The problem is, nothing happens!  The animation works if I change the "DropShadowEffect" to "UIElement" in the Storyboard TargetProperty, but this fades the entire control.</p>
  
  <p>How do I fade just the DropShadowEffect?</p>