WPF数据网格中的单个单元格背景颜色不是所有行颜色

<Window x:Class="WpfApp.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="WPF DataGrid Example" Height="450" Width="800">
    <Grid>
        <DataGrid ItemsSource="{Binding Data}" AutoGenerateColumns="False">
            <DataGrid.Columns>
                <DataGridTextColumn Header="Name" Binding="{Binding Name}">
                    <DataGridTextColumn.CellStyle>
                        <Style TargetType="DataGridCell">
                            <Style.Triggers>
                                <DataTrigger Binding="{Binding Name}" Value="John">
                                    <Setter Property="Background" Value="Yellow"/>
                                </DataTrigger>
                            </Style.Triggers>
                        </Style>
                    </DataGridTextColumn.CellStyle>
                </DataGridTextColumn>
                <DataGridTextColumn Header="Age" Binding="{Binding Age}"/>
            </DataGrid.Columns>
        </DataGrid>
    </Grid>
</Window>