remove square from scrollbar wpf

<Style TargetType="{x:Type ScrollViewer}">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="{x:Type ScrollViewer}">
                <Grid>
                    <Grid.ColumnDefinitions>
                        <ColumnDefinition/>
                        <ColumnDefinition Width="Auto"/>
                    </Grid.ColumnDefinitions>
                    <Grid.RowDefinitions>
                        <RowDefinition/>
                        <RowDefinition Height="Auto"/>
                    </Grid.RowDefinitions>
                    <ScrollContentPresenter Grid.Column="0" />
                    <ScrollBar x:Name="PART_VerticalScrollBar" Grid.Row="0" Grid.Column="1" Value="{TemplateBinding VerticalOffset}" Maximum="{TemplateBinding ScrollableHeight}" ViewportSize="{TemplateBinding ViewportHeight}" Visibility="{TemplateBinding ComputedVerticalScrollBarVisibility}"/>
                    <ScrollBar x:Name="PART_HorizontalScrollBar" Orientation="Horizontal" Grid.Row="1" Grid.Column="0" Value="{TemplateBinding HorizontalOffset}" Maximum="{TemplateBinding ScrollableWidth}" ViewportSize="{TemplateBinding ViewportWidth}" Visibility="{TemplateBinding ComputedHorizontalScrollBarVisibility}"/>
                    <!--<Rectangle Grid.Row="1" Grid.Column="1" Fill="Red"/>-->
                </Grid>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>