c# listbox无法显示边框,如何解决?

wpf中listbox外边框,无论怎么设置都无法显示出来,不知道怎么解决。


```c#
 <ListBox x:Name="listbox" Margin="323,65,616,307" BorderThickness="2"  BorderBrush="Black" >
            <ListBox.Template>
                <ControlTemplate TargetType="{x:Type ListBox}">
                    <ScrollViewer HorizontalScrollBarVisibility="Disabled" VerticalScrollBarVisibility="Auto">
                        <WrapPanel Orientation="Horizontal" IsItemsHost="True" ScrollViewer.CanContentScroll="True"/>
                    ScrollViewer>
                ControlTemplate>
            ListBox.Template>
        ListBox>


```