Avalonia/samples/ControlCatalog/MainWindow.xaml

<Window xmlns="https://github.com/avaloniaui" MinWidth="500" MinHeight="300"        
        xmlns:pages="clr-namespace:ControlCatalog.Pages"
        Title="Avalonia Control Gallery"
        Icon="/Assets/test_icon.ico"
        xmlns:local="clr-namespace:ControlCatalog"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:vm="clr-namespace:ControlCatalog.ViewModels"
        xmlns:v="clr-namespace:ControlCatalog.Views"
        ExtendClientAreaToDecorationsHint="{Binding ExtendClientAreaEnabled}"
        ExtendClientAreaChromeHints="{Binding ChromeHints}"
        ExtendClientAreaTitleBarHeightHint="{Binding TitleBarHeight}"
        TransparencyLevelHint="AcrylicBlur"
        x:Name="MainWindow"
        
        x:Class="ControlCatalog.MainWindow" WindowState="{Binding WindowState, Mode=TwoWay}" Background="{x:Null}">
  <Panel DockPanel.Dock="Left" Width="400" Height="400" Background="Green">

    <Button Content="{Binding Test}" Background="Red" FontSize="55" Foreground="White" VerticalAlignment="Center" HorizontalAlignment="Center"/>
    <Panel>
      <Panel.Background>
        <AcrylicBrush TintColor="Black" BackgroundSource="BackDrop" TintOpacity="0.0" TintLuminosityOpacity="0.4" />
      </Panel.Background>
    </Panel>
  </Panel>
</Window>