How do StyleTriggers work?

I defined the following resources:

    <DataTemplate x:Key="DragTemplate">
        <Grid>
            <Grid.RowDefinitions>
                <RowDefinition Height="40"></RowDefinition>
            </Grid.RowDefinitions>
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="auto"></ColumnDefinition>
            </Grid.ColumnDefinitions>

            <Label x:Name="DraggingSourceLabel" Content="{Binding Name}" BorderThickness="2" BorderBrush="White" Foreground="White" VerticalContentAlignment="Center" HorizontalContentAlignment="Center" Grid.Row="0" Grid.Column="0" FontSize="20"></Label>
        </Grid>
    </DataTemplate>

    <Style x:Key="CursorStyle" TargetType="{x:Type ContentControl}">
        <Setter Property="Opacity" Value="0.50"/>
        <Setter Property="Background" Value"Black"/>
        <Setter Property="ContentTemplate" Value="{StaticResource DragTemplate}" />
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type ContentControl}">
            开发者_Python百科        <ContentPresenter 
                        Content="{TemplateBinding Content}" 
                        ContentTemplate="{TemplateBinding ContentTemplate}">
                    </ContentPresenter>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
        <Style.Triggers>
            <Trigger Property="Tag"  Value="DragEnter">
                <Setter Property="Opacity" Value="1.0"/>
                <Setter Property="Background" Value="Red"/>
            </Trigger>
        </Style.Triggers>
    </Style>

</s:SurfaceWindow.Resources>

But unfortunately, the StyleTriggers aren't working how I thought. The Opacity is changed, but the Background is still the same. I also tried it with only one setter, but the background still didn't changed:

<Style.Triggers>
                <Trigger Property="Tag"  Value="DragEnter">

                    <Setter Property="Background" Value="Red"/>
                </Trigger>
            </Style.Triggers>

What's the problem here?

===EDIT===

Here the code I use to get the ContentControl:

ContentControl cursorVisual = new ContentControl()
                {
                    Content = data,
                    Style = window.FindResource("CursorStyle") as Style

                };

                List<InputDevice> devices = new List<InputDevice>();
                devices.Add(e.Contact);


                ItemsControl dragSource = ItemsControl.ItemsControlFromItemContainer(draggedElement);

                bool startDragOkay = SurfaceDragDrop.BeginDragDrop(sender as Grid, draggedElement, cursorVisual, data, devices, DragDropEffects.Move);      

                if (startDragOkay)
                {
                    e.Handled = true;
                    //draggedElement.Visibility = Visibility.Hidden;
                }

---

Style can't set Background because this property, unlike Opacity, isn't exist in a FrameworkElement class. Properties of a Framework element may be used out of the box, but properties of a Control (such as Background, BorderThickness, HorizontalContentAlignment) should be defined inside a template.

Here is a correct version, I've added a border with background:

<ControlTemplate TargetType="{x:Type ContentControl}">
    <Border Background="{TemplateBinding Background}">
        <ContentPresenter
            Content="{TemplateBinding Content}" 
            ContentTemplate="{TemplateBinding ContentTemplate}">
        </ContentPresenter>
    </Border>
</ControlTemplate>