UWP - RelativePanel stretch example

MainPage.xaml

<Page
    x:Class="UniversalAppTutorials.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:UniversalAppTutorials"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    >
    <RelativePanel Background="AliceBlue" Padding="50">
        <!-- 
            Stretch element horizontally,
            parent left to right edge.
        -->
        <Rectangle
            x:Name="Red"
            Fill="Red"
            Height="50"
            RelativePanel.AlignLeftWithPanel="True"
            RelativePanel.AlignRightWithPanel="True"
            />
        <!-- 
            Stretch element vertically,
            parent top to bottom edge.
        -->
        <Rectangle
            x:Name="Green"
            Fill="Green"
            Width="40"
            RelativePanel.AlignRightWithPanel="True"
            RelativePanel.AlignTopWithPanel="True"
            RelativePanel.AlignBottomWithPanel="True"
            />
        <Rectangle
            x:Name="Blue"
            Fill="Blue"
            Height="30"
            RelativePanel.AlignBottomWithPanel="True"
            RelativePanel.AlignLeftWithPanel="True"
            RelativePanel.AlignRightWithPanel="True"
            />
        <Rectangle
            x:Name="Yellow"
            Fill="Yellow"
            Width="20"
            RelativePanel.AlignLeftWithPanel="True"
            RelativePanel.AlignTopWithPanel="True"
            RelativePanel.AlignBottomWithPanel="True"
            />
        <TextBox
            x:Name="TextBox1"
            Text="Hello UWP."
            RelativePanel.AlignVerticalCenterWithPanel="True"
            RelativePanel.AlignLeftWithPanel="True"
            RelativePanel.AlignRightWithPanel="True"
            />
    </RelativePanel>
</Page>