selected row color on DataGrid not appear above the cells

According to this picture the color of the selected row does not appear over the cells that have been changed color by Style, but appears in the cells that have not been colored by style i want to set it over the cells that have been changed color by Style

<DataGridTextColumn Header=" 8 --- 7 " Binding="{Binding From_7_To_8}">
    <DataGridTextColumn.CellStyle>
        <Style TargetType="{x:Type DataGridCell}" >
            <Setter Property="ContentTemplate">
                <Setter.Value>
                    <DataTemplate>
                        <CheckBox x:Name="C8" Click="CHECK_CLICK"
                                  Style="{DynamicResource CheckBoxStyle1}"
                                  IsEnabled="{Binding  Converter={StaticResource IsEnabled_Cell},ConverterParameter=C8}"
                                  IsChecked="{Binding From_7_To_8,Mode=TwoWay,UpdateSourceTrigger=PropertyChanged}"
                                  FontSize="12"  Content="  7 --- 8  "
                                  HorizontalAlignment="Stretch"
                                  VerticalAlignment="Stretch"
                                  FlowDirection="LeftToRight"
                                  HorizontalContentAlignment="Center" VerticalContentAlignment="Center">
                        </CheckBox>
                    </DataTemplate>
                </Setter.Value>
            </Setter>
            <Style.Triggers>
                <DataTrigger Binding="{Binding Path=Content.IsChecked, RelativeSource={RelativeSource Self}}"
                             Value="false" >
                    <Setter Property="Background" Value="{x:Null}"/>
                </DataTrigger>
                <DataTrigger Binding="{Binding Order_Life_7_8,Mode=TwoWay}" Value="0">
                    <Setter Property="Background" Value="{Binding RelativeSource={RelativeSource Self}}"/>
                </DataTrigger>
                <DataTrigger Binding="{Binding Order_Life_7_8,Mode=TwoWay}" Value="1">
                    <Setter Property="Background" Value="Yellow"/>
                </DataTrigger>
                <DataTrigger Binding="{Binding Order_Life_7_8,Mode=TwoWay}" Value="2">
                    <Setter Property="Background" Value="GreenYellow"/>
                </DataTrigger>
                <DataTrigger Binding="{Binding Order_Life_7_8,Mode=TwoWay}" Value="3">
                    <Setter Property="Background" Value="Yellow"/>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </DataGridTextColumn.CellStyle>
</DataGridTextColumn>