CaritasApp/CaritasApp.UWP/MainPage.xaml

<forms:WindowsPage
    x:Class="CaritasApp.UWP.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:forms="using:Xamarin.Forms.Platform.UWP"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:CaritasApp.UWP"
    Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">

    <Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">

    </Grid>
</forms:WindowsPage>