为什么窗口背景的样式设置不起作用？

Here is the App.xaml:

这是App.xaml：

<Application>
<Application.Resources>
    <ResourceDictionary>
        <Style TargetType="Window">
            <Setter Property="SnapsToDevicePixels" Value="True"/>
            <Setter Property="Background" Value="{DynamicResource {x:Static SystemColors.ControlBrushKey}}"/>
        </Style>
    </ResourceDictionary>
</Application.Resources>
</Application>
<Applicat