XamarinDevDays/Demos/app-tasks/DevDaysTasks.UWP/MainPage.xaml

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

    </Grid>
</forms:WindowsPage>