message: Smoothen close caption button animation
  The red close button animation fades to gray then to transparent, when
  standard behavior skips the gray part. I manually tested in light/dark/high
  contrast mode.
  Closes
diff: Color="#f1707a" />
  <SolidColorBrush x:Key="CloseButtonStrokePressed"
  Color="Black" />
  + <SolidColorBrush x:Key="CloseButtonBackground"
  + Color="#00e81123" />
  + <Color x:Key="CloseButtonBackgroundColor">#00e81123</Color>
  </ResourceDictionary>
  <ResourceDictionary x:Key="Dark">
  <x:Double x:Key="CaptionButtonStrokeWidth">1.0</x:Double>
  Color="#f1707a" />
  <SolidColorBrush x:Key="CloseButtonStrokePressed"
  Color="Black" />
  + <SolidColorBrush x:Key="CloseButtonBackground"
  + Color="#00e81123" />
  + <Color x:Key="CloseButtonBackgroundColor">#00e81123</Color>
  </ResourceDictionary>
  <ResourceDictionary x:Key="HighContrast">
  <x:Double x:Key="CaptionButtonStrokeWidth">3.0</x:Double>
  ResourceKey="CloseButtonStrokePointerOver" />
  <StaticResource x:Key="CaptionButtonStrokePressed"
  ResourceKey="CloseButtonStrokePressed" />
  + <StaticResource x:Key="CaptionButtonBackground"
  + ResourceKey="CloseButtonBackground" />
  + <StaticResource x:Key="CaptionButtonBackgroundColor"
  + ResourceKey="CloseButtonBackgroundColor" />
  </ResourceDictionary>
  <ResourceDictionary x:Key="Dark">
  <StaticResource x:Key="CaptionButtonBackgroundPointerOver"
  ResourceKey="CloseButtonStrokePointerOver" />
  <StaticResource x:Key="CaptionButtonStrokePressed"
  ResourceKey="CloseButtonStrokePressed" />
  + <StaticResource x:Key="CaptionButtonBackground"
  + ResourceKey="CloseButtonBackground" />
  + <StaticResource x:Key="CaptionButtonBackgroundColor"
  + ResourceKey="CloseButtonBackgroundColor" />
  </ResourceDictionary>
  <ResourceDictionary x:Key="HighContrast">
  <StaticResource x:Key="CaptionButtonBackgroundPointerOver"
  