WPF 透明背景窗体

<Window x:Class="WpfApplication8.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" AllowsTransparency="True"
        Background="Transparent" WindowStyle="None" BorderThickness="0" MouseLeftButtonDown="Window_MouseLeftButtonDown"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Border Background="Pink"  BorderThickness="5" BorderBrush="Beige" Margin="0,0,409,0"></Border>

        <Border Background="#8CFDFDFD" BorderThickness="1" HorizontalAlignment="Center" BorderBrush="WhiteSmoke" Margin="2,0,2,23" MinHeight="55" MinWidth="22" MaxWidth="222" VerticalAlignment="Bottom">
            <Border.Effect>
                <DropShadowEffect Color="#70FAEBD7" />
            </Border.Effect>
                <Grid>
                <TextBlock Name="txt" Padding="12" VerticalAlignment="Center" FontSize="14"  FontWeight="Bold" Foreground="#FFFF8888" TextWrapping="Wrap" Text="-----">
                    <TextBlock.Effect>
                         <DropShadowEffect Color="#70FFFFFF" />
                    </TextBlock.Effect>
                </TextBlock>
            </Grid>
        </Border>

    </Grid>
</Window>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
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.Navigation;
using System.Windows.Shapes;

namespace WpfApplication8
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
            work();
        }

        private void Window_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
        {
            DragMove();
        }

       void work() {

             Task.Run(() => {
                while (true)
                {

                    Dispatcher.Invoke(() =>
                    {

                        txt.Text = "梵蒂冈冈梵蒂冈法定" + DateTime.Now;

                    });

                    Thread.Sleep(1000);
                }

            });

        }

    }
}