如何修改WPF数据网格中DataGridSelectAllButton下的按钮宽度?

我需要修改 Width 属于 DataGridSelectAllButton 所以我用下面的代码来改变它:

 <ControlTemplate x:Key="DataGridControlTemplate" TargetType="{x:Type DataGrid}">
    <Border BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" Padding="{TemplateBinding Padding}" SnapsToDevicePixels="True">
        <ScrollViewer x:Name="DG_ScrollViewer" Focusable="false">
            <ScrollViewer.Template>
                <ControlTemplate TargetType="{x:Type ScrollViewer}">
                    <Grid>
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition Width="Auto"/>
                            <ColumnDefinition Width="*"/>
                            <ColumnDefinition Width="Auto"/>
                        </Grid.ColumnDefinitions>
                        <Grid.RowDefinitions>
                            <RowDefinition Height="Auto"/>
                            <RowDefinition Height="*"/>
                            <RowDefinition Height="Auto"/>
                        </Grid.RowDefinitions>
                        <Button Style="{DynamicResource {ComponentResourceKey ResourceId=DataGridSelectAllButtonStyle, TypeInTargetAssembly={x:Type DataGrid}}}" 
                                    Visibility="{Binding HeadersVisibility, ConverterParameter={x:Static DataGridHeadersVisibility.All}, Converter={x:Static DataGrid.HeadersVisibilityConverter}, RelativeSource={RelativeSource AncestorType={x:Type DataGrid}}}" 
                                    **Width="20"**>
                        </Button>
                        <DataGridColumnHeadersPresenter x:Name="PART_ColumnHeadersPresenter" Grid.Column="1" Visibility="{Binding HeadersVisibility, ConverterParameter={x:Static DataGridHeadersVisibility.Column}, Converter={x:Static DataGrid.HeadersVisibilityConverter}, RelativeSource={RelativeSource AncestorType={x:Type DataGrid}}}"/>
                        <ScrollContentPresenter x:Name="PART_ScrollContentPresenter" CanContentScroll="{TemplateBinding CanContentScroll}" Grid.ColumnSpan="2" Grid.Row="1" d:IsLocked="True"/>
                        <ScrollBar x:Name="PART_VerticalScrollBar" Grid.Column="2" Maximum="{TemplateBinding ScrollableHeight}" Orientation="Vertical" Grid.Row="1" Visibility="{TemplateBinding ComputedVerticalScrollBarVisibility}" Value="{Binding VerticalOffset, Mode=OneWay, RelativeSource={RelativeSource TemplatedParent}}" ViewportSize="{TemplateBinding ViewportHeight}" d:IsLocked="True"/>
                        <Grid Grid.Column="1" Grid.Row="2" d:IsLocked="True">
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition Width="{Binding NonFrozenColumnsViewportHorizontalOffset, RelativeSource={RelativeSource AncestorType={x:Type DataGrid}}}"/>
                                <ColumnDefinition Width="*"/>
                            </Grid.ColumnDefinitions>
                            <ScrollBar x:Name="PART_HorizontalScrollBar" Grid.Column="1" Maximum="{TemplateBinding ScrollableWidth}" Orientation="Horizontal" Visibility="{TemplateBinding ComputedHorizontalScrollBarVisibility}" Value="{Binding HorizontalOffset, Mode=OneWay, RelativeSource={RelativeSource TemplatedParent}}" ViewportSize="{TemplateBinding ViewportWidth}" d:IsLocked="True"/>
                        </Grid>
                    </Grid>
                </ControlTemplate>
            </ScrollViewer.Template>
            <ItemsPresenter  SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"/>
        </ScrollViewer>
    </Border>
</ControlTemplate>

问题是当我改变 宽度 的 数据网格全选按钮 ,我必须更改的宽度 Buttom ,放置在 数据网格全选按钮 每一排也是,但我不知道怎么做?有什么想法吗?