WPF - przyciemnienie okna z zaokrąglonymi rogami

<ResourceDictionary xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

    <Storyboard x:Key="StoryboardOpacityDown">
        <DoubleAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetName="{x:Null}" Storyboard.TargetProperty="(UIElement.Opacity)">
            <SplineDoubleKeyFrame KeyTime="00:00:00.3" Value="0.4"/>
        </DoubleAnimationUsingKeyFrames>
    </Storyboard>
    <Storyboard x:Key="StoryboardOpacityUp">
        <DoubleAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetName="{x:Null}" Storyboard.TargetProperty="(UIElement.Opacity)">
            <SplineDoubleKeyFrame KeyTime="00:00:00.3" Value="1"/>
        </DoubleAnimationUsingKeyFrames>
    </Storyboard>

    <Style x:Key="SubWindowStyle" TargetType="{x:Type Window}">
        <Setter Property="WindowStyle" Value="None"/>
        <Setter Property="ResizeMode" Value="NoResize"/>
        <Setter Property="AllowsTransparency" Value="True"/>
        <Setter Property="ShowInTaskbar" Value="False"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type Window}">
                    <Grid>
                        <Border CornerRadius="10" Background="Crimson">
                            <ContentPresenter/>
                        </Border>
                    </Grid>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</ResourceDictionary>

<Window x:Class="WpfApplication1.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525"
        WindowState="Maximized">  
    
    <Grid>
        <Border Background="LightBlue">
            <StackPanel Orientation="Horizontal">
                <Border Height="300" Width="300" Background="White" HorizontalAlignment="Left"/>
                <Button Height="30" Width="80" Content="Nowe okno" HorizontalAlignment="Left" Click="Button_Click"/>
            </StackPanel>
        </Border>
    </Grid>
</Window>

 
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using System.Windows.Media.Animation;

namespace WpfApplication1
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            ((Storyboard)FindResource("StoryboardOpacityDown")).Begin(this);
                ChildWindow childWindow = new ChildWindow();
                childWindow.ShowDialog();
            ((Storyboard)FindResource("StoryboardOpacityUp")).Begin(this);

        }
    }
}

<Window x:Class="WpfApplication1.ChildWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="ChildWindow" Height="300" Width="300"
        MouseLeftButtonDown="DragWindow_MouseLeftButtonDown"
        Style="{DynamicResource SubWindowStyle}">    

    <Grid>
        <StackPanel Orientation="Vertical">
            <Button Height="30" Width="80" Content="Nowe okno" HorizontalAlignment="Left" Margin="0,20,0,0" Click="Button_Click"/>
            <Button Height="30" Width="80" Content="Zamknij" HorizontalAlignment="Left" Margin="0,20,0,0" Click="Button2_Click"/>
        </StackPanel>
    </Grid>
</Window>

 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Shapes;
using System.Windows.Media.Animation;
using System.Windows;

namespace WpfApplication1
{
    /// <summary>
    /// Interaction logic for ChildWindow.xaml
    /// </summary>
    public partial class ChildWindow : Window
    {
        public ChildWindow()
        {
            InitializeComponent();
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            ((Storyboard)FindResource("StoryboardOpacityDown")).Begin(this);
                MessageBox.Show("Nowe okno");
            ((Storyboard)FindResource("StoryboardOpacityUp")).Begin(this);
        }

        private void Button2_Click(object sender, RoutedEventArgs e)
        {
            this.Close();
        }

        private void DragWindow_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
        {
            this.DragMove();
        }
    }
}

<Application.Resources>
    <ResourceDictionary>
        <ResourceDictionary.MergedDictionaries>
            <ResourceDictionary Source="Dictionary.xaml"/>
        </ResourceDictionary.MergedDictionaries>
    </ResourceDictionary>         
</Application.Resources>

<Storyboard x:Key="StoryboardOpacityDown">
	<DoubleAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetName="{x:Null}" Storyboard.TargetProperty="(UIElement.Opacity)">
		<SplineDoubleKeyFrame KeyTime="00:00:00.3" Value="0.6"/>
	</DoubleAnimationUsingKeyFrames>
</Storyboard>
<Storyboard x:Key="StoryboardOpacityUp">
	<DoubleAnimationUsingKeyFrames BeginTime="00:00:00" Storyboard.TargetName="{x:Null}" Storyboard.TargetProperty="(UIElement.Opacity)">
		<SplineDoubleKeyFrame KeyTime="00:00:00.3" Value="0"/>
	</DoubleAnimationUsingKeyFrames>
</Storyboard>

<Grid>
	<StackPanel Orientation="Vertical">
	......
	</StackPanel>
	<Border CornerRadius="10"   x:Name="FajowyCzarnyPanel" IsHitTestVisible="False" Background="Black"   Opacity="0" />
</Grid>

((Storyboard)FindResource("StoryboardOpacityDown")).Begin(FajowyCzarnyPanel);
MessageBox.Show("Nowe okno");
((Storyboard)FindResource("StoryboardOpacityUp")).Begin(FajowyCzarnyPanel);