ui/winui/MainWindow.xaml

<?xml version="1.0" encoding="utf-8"?>
<Window
    x:Class="winui.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:winui"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">

    <Window.SystemBackdrop>
        <MicaBackdrop />
    </Window.SystemBackdrop>

    <Grid RowDefinitions="Auto, Auto" ColumnDefinitions="*"  Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
        <StackPanel x:Name="AppTitleBar" Orientation="Horizontal" Grid.Column="0" Grid.Row="0" Padding="10,5,5,10">
            <TextBlock x:Name="AppTitleTextBlock" Text="Window Title" CanDrag="True"></TextBlock>
        </StackPanel>
    </Grid>
</Window>