สอบถามหน่อยครับ มือใหม่จริงๆ ครับ the resource "ApplicationPageBackgroundThemeBrush" could not be resolve

<Page
    x:Class="App4.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:App4"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">

     <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">

        <TextBlock x:Name="lblResult" HorizontalAlignment="Left" Margin="66,83,0,0" TextWrapping="Wrap" VerticalAlignment="Top" FontSize="20" Text="lblResult"/>

    </Grid>

</Page>