【WPF】DataGrid修改左上角全选的按钮样式

<Style TargetType="{x:Type DataGrid}">
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type DataGrid}">
                        <Border x:Name="border"
                SnapsToDevicePixels="True"
                BorderBrush="{TemplateBinding BorderBrush}"
                BorderThickness="{TemplateBinding BorderThickness}"
                Padding="{TemplateBinding Padding}">
                            <Border.Background>
                                <SolidColorBrush Color="White" />
                            </Border.Background>
                            <ScrollViewer x:Name="DG_ScrollViewer"
                        Focusable="false"
                        Background="Black">
                                <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 Focusable="false"
                          Command="{x:Static DataGrid.SelectAllCommand}"
                          Visibility="{Binding HeadersVisibility, 
                      ConverterParameter={x:Static DataGridHeadersVisibility.All}, 
                      Converter={x:Static DataGrid.HeadersVisibilityConverter}, 
                      RelativeSource={RelativeSource AncestorType={x:Type DataGrid}}}"
                          Width="{Binding CellsPanelHorizontalOffset, 
                      RelativeSource={RelativeSource AncestorType={x:Type DataGrid}}}" BorderBrush="LightGray" Background="Yellow"/>
                                            <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"
                                          Grid.ColumnSpan="2"
                                          Grid.Row="1"
                                          CanContentScroll="{TemplateBinding CanContentScroll}" />
                                            <ScrollBar x:Name="PART_VerticalScrollBar"
                             Grid.Column="2"
                             Grid.Row="1"
                             Orientation="Vertical"
                             ViewportSize="{TemplateBinding ViewportHeight}"
                             Maximum="{TemplateBinding ScrollableHeight}"
                             Visibility="{TemplateBinding ComputedVerticalScrollBarVisibility}"
                             Value="{Binding VerticalOffset, Mode=OneWay, 
                      RelativeSource={RelativeSource TemplatedParent}}"/>
                                            <Grid Grid.Column="1"
                        Grid.Row="2">
                                                <Grid.ColumnDefinitions>
                                                    <ColumnDefinition Width="{Binding NonFrozenColumnsViewportHorizontalOffset, 
                          RelativeSource={RelativeSource AncestorType={x:Type DataGrid}}}" />
                                                    <ColumnDefinition Width="*" />
                                                </Grid.ColumnDefinitions>
                                                <ScrollBar x:Name="PART_HorizontalScrollBar"
                               Grid.Column="1"
                               Orientation="Horizontal"
                               ViewportSize="{TemplateBinding ViewportWidth}"
                               Maximum="{TemplateBinding ScrollableWidth}"
                               Visibility="{TemplateBinding ComputedHorizontalScrollBarVisibility}"
                               Value="{Binding HorizontalOffset, Mode=OneWay, 
                        RelativeSource={RelativeSource TemplatedParent}}"/>
                                            </Grid>
                                        </Grid>
                                    </ControlTemplate>
                                </ScrollViewer.Template>
                                <ItemsPresenter SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}" />
                            </ScrollViewer>
                        </Border>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
        <Style TargetType="{x:Type DataGridColumnHeader}">
            <Setter Property="VerticalContentAlignment"
          Value="Center" />
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="{x:Type DataGridColumnHeader}">
                        <Border x:Name="columnHeaderBorder"
                  BorderThickness="1"
             BorderBrush="LightGray"
                                Background="Yellow" MinHeight="30" MinWidth="60">
                            <ContentPresenter HorizontalAlignment="Center"
                              SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"
                              VerticalAlignment="Center" />
                        </Border>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>