无法从应用程序级别获取资源

My app.xaml:

<Application.Resources>
    <RadialGradientBrush x:Key="myBrush">
        <GradientStop Color="#FFC44EC4" Offset="0" />
        <GradientStop Color="#FF829CEB" Offset="1" />
        <GradientStop Color="#FF793879" Offset="0.669" />
    </RadialGradientBrush>
</Application.Resources>
<Application.Resources>
    <Rad