Animate a Border size based on on the target control size

AnimatedSize.xaml

<Panel>
  
  <Border x:Name="AnimatedBorder">
    
    <Control x:Name="AnimatedBorderGovernor"
               Fill="Transparent"
               Width="{Binding #Target.Bounds.Width}"
               Height="{Binding #Target.Bounds.Height}"
               >
      <Control.Transitions>
        <Transitions>
          <DoubleTransition Property="Height" Duration="..." Easing="..."/>
          <DoubleTransition Property="Width"  Duration="..." Easing="..."/>
        </Transitions>
      </Control.Transitions>
    </Control>
    
  </Border>
  
  <TransitioningContentControl x:Name="Target"/>
  
</Panel>