Example of in-app acrylic in MSIX Reunion app

MainWindow.xaml

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

    <Grid>
        <Canvas Width="128" Height="128" Background="Gray">
            <Rectangle Fill="Red" Canvas.Left="0" Canvas.Top="0" Canvas.ZIndex="0" Width="32" Height="32" />
            <Rectangle Fill="Blue" Canvas.Left="20" Canvas.Top="20" Canvas.ZIndex="1" Width="32" Height="32" />
            <Rectangle Fill="Green" Canvas.Left="40" Canvas.Top="40" Canvas.ZIndex="2" Width="32" Height="32" />
            <Rectangle Fill="Yellow" Canvas.Left="60" Canvas.Top="60" Canvas.ZIndex="3" Width="32" Height="32" />
            <Rectangle Fill="{ThemeResource SystemControlAcrylicElementBrush}" Canvas.Left="32" Canvas.Top="32" Canvas.ZIndex="4" Width="64" Height="64" />
        </Canvas>
    </Grid>
</Window>

Notice the project is named HelloReunion