<Window x:Class="Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="300" Width="300">
        <Border Margin="0,50,0,0" Background="White" BorderThickness="1" _
          BorderBrush="Black">
            <Grid>
 
            </Grid>
        </Border>
</Window>

Imports System.Windows
Imports System.Runtime.InteropServices
 
Class Window1
 
    Protected Overloads Overrides Sub OnSourceInitialized(ByVal e As EventArgs)
        MyBase.OnSourceInitialized(e)
        GlassSurface.ExtendGlassFrame(Me, New Thickness(-1))
    End Sub
 
End Class
 
Public Class GlassSurface
    <DllImport("dwmapi.dll", PreserveSig:=False)> _
    Private Shared Sub DwmExtendFrameIntoClientArea(ByVal hwnd As IntPtr, ByRef _
    margins As MARGINS)
    End Sub
 
    <DllImport("dwmapi.dll", PreserveSig:=False)> _
    Private Shared Function DwmIsCompositionEnabled() As Boolean
    End Function
 
    Public Shared Function ExtendGlassFrame(ByVal window As Window, ByVal _
      margin As Thickness) As Boolean
        Try
            If Not DwmIsCompositionEnabled() Then
                Return False
            End If
            Dim hwnd As IntPtr = New Interop.WindowInteropHelper(window).Handle
            If hwnd = IntPtr.Zero Then Return False
            window.Background = Media.Brushes.Transparent
            Interop.HwndSource.FromHwnd(hwnd).CompositionTarget.BackgroundColor _
              = Media.Colors.Transparent
            DwmExtendFrameIntoClientArea(hwnd, New MARGINS(margin))
            Return True
        Catch ex As Exception
            Return False
        End Try
    End Function
End Class
 
Structure MARGINS
    Public Top As Integer
    Public Bottom As Integer
    Public Left As Integer
    Public Right As Integer
    Public Sub New(ByVal t As Thickness)
        Top = CInt(t.Top)
        Bottom = CInt(t.Bottom)
        Left = CInt(t.Left)
        Right = CInt(t.Right)
    End Sub
End Structure