问WPF样式触发器在IsPressed上设置按钮前台，但不设置背景

EN

<Window x:Class="MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:local="clr-namespace:WpfExperiments"
        mc:Ignorable="d"
        Title="MainWindow" Height="350" Width="525">
    <Grid Margin="0,0,0,2">
        <Grid.Resources>
            <Style x:Key="ButtonStyle" TargetType="Button">
                <Style.Triggers>
                    <Trigger Property="IsPressed" Value="True">
                        <Setter Property="Foreground" Value="Red"/>
                        <Setter Property="Background" Value="Red"/>
                    </Trigger>
                </Style.Triggers>
            </Style>
        </Grid.Resources>
        <Button Style="{StaticResource ButtonStyle}" 
                Content="Button"
                HorizontalAlignment="Left"
                Margin="135,97,0,0"
                VerticalAlignment="Top"
                Width="75"
                />
    </Grid>
</Window>