MixerPage.xaml

<Page
    x:Class="OBSAudioMixer.MixerPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:OBSAudioMixer"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d"
    Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">

    <Grid>
        <TextBlock Text=""></TextBlock>
        <ScrollViewer HorizontalScrollMode="Enabled" Width="Auto" HorizontalScrollBarVisibility="Auto">
            <StackPanel x:Name="spMixer" Margin="20" Orientation="Horizontal">
                <!--<Rectangle Fill="Red" Width="150" Height="Auto" Margin="5" />
                <Rectangle Fill="Blue" Width="150" Height="Auto" Margin="5" />
                <Rectangle Fill="Green" Width="150" Height="Auto" Margin="5" />
                <Rectangle Fill="Purple" Width="150" Height="Auto" Margin="5" />-->
            </StackPanel>
        </ScrollViewer>
    </Grid>
</Page>