Xamarin aplication resource style using OnPlatform

Resource.xml

      <Application.Resources>
        <ResourceDictionary>

          <OnPlatform x:TypeArguments="Font" Android="30" iOS="40" WinPhone="20" x:Key="TitleFontSize" />

          <Style x:Key="MyTitleLabel" TargetType="Label" BaseResourceKey="TitleStyle">
            <Setter Property="LineBreakMode" Value="TailTruncation" />
            <Setter Property="XAlign" Value="Center" />
            <Setter Property="Font" Value="{StaticResource TitleFontSize}" />
          </Style>
        </ResourceDictionary>
      </Application.Resources>