未应用全局标签样式

我正在尝试将全局隐式样式添加到所有标签中。我定义了以下样式:

<Style x:Key="LabelStyle" TargetType="{x:Type Label}">
    <Setter Property="Background" Value="Green"></Setter>
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="Label">
                <Viewbox StretchDirection="DownOnly" HorizontalAlignment="Left">
                    <ContentPresenter HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                                      VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
                                      RecognizesAccessKey="True" />
                </Viewbox>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

我尝试将其放入app.xaml文件:

<Application.Resources>
    <ResourceDictionary>
        <Style x:Key="LabelStyle" TargetType="{x:Type Label}">
            <Setter Property="Background" Value="Green"></Setter>
            <Setter Property="Template">
                <Setter.Value>
                    <ControlTemplate TargetType="Label">
                        <Viewbox StretchDirection="DownOnly" HorizontalAlignment="Left">
                            <ContentPresenter HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
                                              VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
                                              RecognizesAccessKey="True" />
                        </Viewbox>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
        </Style>
        <!--Merge Dictionaries...-->
    </ResourceDictionary>
</Application.Resources>

但它似乎没有改变任何东西。我也尝试将它包含在我的主题文件中,但它也不起作用。我试着在一个新项目中这样做,看看在我当前的项目中是否有任何不同风格的冲突,但似乎不是这样。