WPF弹出窗口，底部仅有圆角

<Window x:Class="WpfApp1.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"
        AllowsTransparency="True" WindowStyle="None" Background="Transparent">
    <Grid>
        <Border Background="White" CornerRadius="0,0,10,10">
            <Grid>
                <!-- Your content here -->
            </Grid>
        </Border>
    </Grid>
</Window>