WPF 圆角textbox

<Window x:Class="WpfApplication1.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">
<Grid>
<Border CornerRadius="5" Height="35" Margin="142,137,202,139" BorderThickness="1" BorderBrush="#FF737070">
<TextBox Height="32" Name="textBox1" Width="156" Background="{x:Null}" BorderThickness="0" FontSize="22" />
</Border>
</Grid>
</Window>