Windows Presentation Foundation в .NET 4. День 61 - 402 стр. Основы анимации

<DockPanel LastChildFill="True">
    <StackPanel DockPanel.Dock="Top" Orientation="Horizontal" Height="70" VerticalAlignment="Top" HorizontalAlignment="Center">
        <Ellipse Name="el1" Height="50" Width="50" Fill="DarkOrange" MouseEnter="btn_MouseEnter" MouseLeave="btn_MouseLeave"/>
        <Ellipse Height="50" Width="50" Fill="DarkOrange" MouseEnter="btn_MouseEnter" MouseLeave="btn_MouseLeave"/>
        <Ellipse Height="50" Width="50" Fill="DarkOrange" MouseEnter="btn_MouseEnter" MouseLeave="btn_MouseLeave"/>
        <Ellipse Height="50" Width="50" Fill="DarkOrange" MouseEnter="btn_MouseEnter" MouseLeave="btn_MouseLeave"/>
    </StackPanel>
.............
</DockPanel>

private const double animationDuration = 100;
        private const double increaseSize = 20;
        private const double DRatioKoef = 0.9;
 
        private void btn_MouseEnter (object sender, System.Windows.Input.MouseEventArgs e) {
            UIElement element = (UIElement) sender;
            DoubleAnimation widthAnimation = new DoubleAnimation();
            widthAnimation.By = increaseSize;
            widthAnimation.DecelerationRatio = DRatioKoef;
            widthAnimation.Duration = TimeSpan.FromMilliseconds(animationDuration);
            DoubleAnimation heightAnimation = new DoubleAnimation();
            heightAnimation.By = increaseSize;
            heightAnimation.DecelerationRatio = DRatioKoef;
            heightAnimation.Duration = TimeSpan.FromMilliseconds(animationDuration);
            element.BeginAnimation(WidthProperty, widthAnimation);
            element.BeginAnimation(HeightProperty, heightAnimation);
        }
 
        private void btn_MouseLeave (object sender, System.Windows.Input.MouseEventArgs e) {
            UIElement element = (UIElement)sender;
            DoubleAnimation widthAnimation = new DoubleAnimation();
            widthAnimation.Duration = TimeSpan.FromMilliseconds(animationDuration);
            DoubleAnimation heightAnimation = new DoubleAnimation();
            heightAnimation.Duration = TimeSpan.FromMilliseconds(animationDuration);
            element.BeginAnimation(WidthProperty, widthAnimation);
            element.BeginAnimation(HeightProperty, heightAnimation);
        }