<Window x:Class="Walterlv.Demo.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:interop="clr-namespace:Walterlv.Demo.Interop"
    mc:Ignorable="d" Title="AboutDlg" Height="350" Width="525"
    interop:WindowBlur.IsEnabled="True"
    Background="Transparent">
</Window>

public class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
        WindowBlur.SetIsEnabled(this, true);
    }
}