Comment faire une grille de coin arrondie?

J'ai essayé et il établit une nouvelle frontière au-dessus de la bordure de la grille:

<Window x:Class="Class.Window"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Window1" Width="379" Loaded="Window_Loaded"
        AllowsTransparency="True"
        ResizeMode="NoResize" ShowInTaskbar="False" Topmost="True" WindowStyle="None" Height="110">    
    <Border BorderBrush="Black" BorderThickness="1,1,1,1" CornerRadius="30,30,30,30">
        <Grid>
            <TextBlock Height="23" HorizontalAlignment="Left" Margin="62,12,0,0" Name="textBlock_From" Text="" VerticalAlignment="Top" Width="283" />
            <TextBlock Height="23" HorizontalAlignment="Left" Margin="62,38,0,0" Name="textBlock_Subject" Text="" VerticalAlignment="Top" Width="283" 
                       MouseLeftButtonDown="textBlock_Subject_MouseLeftButtonDown" MouseEnter="textBlock_Subject_MouseEnter" MouseLeave="textBlock_Subject_MouseLeave" />
        </Grid>
    </Border>
</Window>

source d'informationauteur Alex Kapustian