private void btn4_MouseEnter(object sender, MouseEventArgs e)
        {
            StackPanel1.Visibility = Visibility.Hidden;
            StackPanel2.Visibility = Visibility.Hidden;
            StackPanel3.Visibility = Visibility.Visible;
            StackPanel4.Visibility = Visibility.Hidden;
            czy_otwarta_pierwsza   = false;
            czy_otwarta_druga      = false;
            czy_otwarta_trzecia    = true;
            czy_otwarta_czwarta    = false;

            Rectangle3.BeginAnimation(WidthProperty, BorderAnimation1);
        }
 private void btn3_MouseEnter(object sender, MouseEventArgs e)
 {
     if (StackPanel3.Visibility == Visibility.Hidden)
     {
         StackPanel3.BeginAnimation(HeightProperty, DropDownAnimation);
         StackPanel3.BeginAnimation(OpacityProperty, DropDownOpacityAnimation);
         StackPanel3.Effect.BeginAnimation(OpacityProperty, DropDownOpacityAnimation);
     }
     StackPanel1.Visibility = Visibility.Hidden;
     StackPanel2.Visibility = Visibility.Hidden;
     StackPanel3.Visibility = Visibility.Visible;
     StackPanel4.Visibility = Visibility.Hidden;
     Rectangle3.BeginAnimation(WidthProperty, BorderAnimation1);
 }
 private void btn4_MouseLeave(object sender, MouseEventArgs e)
 {
     Rectangle3.BeginAnimation(WidthProperty, BorderAnimation2);
 }