How to set default WPF Window Style in app.xaml?

I am trying to set the default Style for every window in my WPF Windows application in my app.xaml. So far i have this in app.xaml:

<Application.Resources>
    <ResourceDictionary>
        <Style x:Key="WindowStyle" TargetType="{x:Type Window}">
            <Setter Property="Background" Value="Blue" />
        </Style>
    </ResourceDictionary>
</Application.Resources>

I can get the window to appear with this style when running the app (but not in VS designer) by specifically telling the window to use this style via:

Style="{DynamicResource WindowStyle}

This works, but is not ideal. So how do I:

1. Have all windows automatically use the style (so i don't have to specify it on every window)?
2. Have VS designer show the style?

Thanks!