WPF，怎么把GroupBox外面的矩形框替换成另一种样式？

Question

一个dll里面的一个矩形框：
<SketchControls:SketchRectangleUC />我想把GroupBox外面的矩形框替换成这个矩形框，怎么操作高手help?
使用这个样式时出现问题，<GroupBox.Header>里面的内容无法显示。<Style x:Key="GroupBox-Sketch" TargetType="{x:Type GroupBox}">
    <Setter Property="FontSize" Value="{DynamicResource SizeDouble-Sketch}"/>
    <Setter Property="Foreground" Value="{DynamicResource BaseForeground-Sketch}"/>
    <Setter Property="Padding" Value="4,4,4,4"/>
    <Setter Property="BorderThickness" Value="2"/>
    <Setter Property="Foreground" Value="{StaticResource BaseBorder-Sketch}"/>
    <Setter Property="BorderBrush" Value="{StaticResource BaseBorder-Sketch}"/>
    <Setter Property="Background" Value="{StaticResource BaseBackground-Sketch}"/>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type GroupBox}">
                <Grid>
                    <SketchControls:SketchRectangleUC x:Name="SketchRectangleUC"  HorizontalAlignment="Stretch" BorderBrush="{TemplateBinding BorderBrush}" VerticalAlignment="Stretch" StrokeWidth="2" ExtensionLength="0" ExtensionVariance="0" SegmentLength="8" SegmentOffset="0.8" SegmentVariance="0.1" Background="{TemplateBinding Background}" Foreground="{TemplateBinding Foreground}"/>
                    <ContentPresenter SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" Margin="5,5,5,5" x:Name="PART_SelectedContentHost"/>
                </Grid>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>