public partial class MainWindow : Window
    {

        public MainWindow()
        {
            InitializeComponent();

            Opacity = 0;
            Loaded += (o,e) => FadeIn();

        }

        private void Window_Closing(object sender, CancelEventArgs e)
        {
            Closing -= Window_Closing;
            e.Cancel = true;

            DoubleAnimation fadeOut = new DoubleAnimation(0, TimeSpan.FromMilliseconds(350));
            fadeOut.Completed += (s, _) => Close();
            BeginAnimation(OpacityProperty, fadeOut);
        }

        private void FadeIn()
        {
            DoubleAnimation fadeIn = new DoubleAnimation(1, TimeSpan.FromSeconds(2));
            DoubleAnimation scaleWidth = new DoubleAnimation(Width, Width * 1.1, TimeSpan.FromSeconds(2));
            DoubleAnimation scaleHeight = new DoubleAnimation(Height, Height * 1.1, TimeSpan.FromSeconds(2));

            BeginAnimation(OpacityProperty, fadeIn);
            BeginAnimation(WidthProperty, scaleWidth);
            BeginAnimation(HeightProperty, scaleHeight);
        }
    }