Avalonia/samples/ControlCatalog/MainWindow.xaml

<Window xmlns="https://github.com/avaloniaui" MinWidth="500" MinHeight="300"
        Width="1024" Height="800"
        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="{Binding TransparencyLevel}"
        x:Name="MainWindow"
        x:Class="ControlCatalog.MainWindow" WindowState="{Binding WindowState, Mode=TwoWay}" Background="{x:Null}">
  <NativeMenu.Menu>
    <NativeMenu>
      <NativeMenuItem Header="File">
        <NativeMenuItem.Menu>
          <NativeMenu>
            <NativeMenuItem Icon="/Assets/test_icon.ico" Header="Open" Clicked="OnOpenClicked" Gesture="Ctrl+O"/>
            <NativeMenuItemSeperator/>
            <NativeMenuItem Icon="/Assets/github_icon.png" Header="Recent">
              <NativeMenuItem.Menu>
                <NativeMenu/>
              </NativeMenuItem.Menu>
            </NativeMenuItem>
            <NativeMenuItemSeperator/>
            <NativeMenuItem Header="{x:Static local:MainWindow.MenuQuitHeader}"
                            Gesture="{x:Static local:MainWindow.MenuQuitGesture}"
                            Clicked="OnCloseClicked" />
          </NativeMenu>
        </NativeMenuItem.Menu>
      </NativeMenuItem>
      <NativeMenuItem Header="Edit">
        <NativeMenuItem.Menu>
          <NativeMenu>
            <NativeMenuItem Header="Copy"/>
            <NativeMenuItem Header="Paste"/>
          </NativeMenu>
        </NativeMenuItem.Menu>
      </NativeMenuItem>
      <NativeMenuItem Header="Options">
        <NativeMenuItem.Menu>
          <NativeMenu>
           <NativeMenuItem Header="Check Me (None)" 
                            Command="{Binding ToggleMenuItemCheckedCommand}"
                            ToggleType="None"
                            IsChecked="{Binding IsMenuItemChecked}"  />
            <NativeMenuItem Header="Check Me (CheckBox)" 
                            Command="{Binding ToggleMenuItemCheckedCommand}"
                            ToggleType="CheckBox"
                            IsChecked="{Binding IsMenuItemChecked}"  />
            <NativeMenuItem Header="Check Me (Radio)" 
                            Command="{Binding ToggleMenuItemCheckedCommand}"
                            ToggleType="Radio"
                            IsChecked="{Binding IsMenuItemChecked}"  />
          </NativeMenu>
        </NativeMenuItem.Menu>
      </NativeMenuItem>
    </NativeMenu>
  </NativeMenu.Menu>

  <Window.DataTemplates>
    <DataTemplate DataType="vm:NotificationViewModel">
      <v:CustomNotificationView />
    </DataTemplate>
  </Window.DataTemplates>
  <Panel>  
    <Panel Margin="{Binding #MainWindow.OffScreenMargin}">
      <DockPanel LastChildFill="True" Margin="{Binding #MainWindow.WindowDecorationMargins}">
      <Menu Name="MainMenu" DockPanel.Dock="Top">
        <MenuItem Header="File">
          <MenuItem Header="Exit" Command="{Binding ExitCommand}" />
        </MenuItem>
        <MenuItem Header="Help">
          <MenuItem Header="About" Command="{Binding AboutCommand}" />
        </MenuItem>
      </Menu>
      <local:MainView />
    </DockPanel>
    </Panel>    
    <Border BorderThickness="1 1 1 0" CornerRadius="4 4 0 0" BorderBrush="#55000000" Height="22" VerticalAlignment="Top" HorizontalAlignment="Left" Margin="250 8 0 0">
      <Border.Background>
        <SolidColorBrush Color="White" Opacity="0.7" />
      </Border.Background>
      <TextBlock Margin="5 5 5 0" Text="Content In TitleBar" />
    </Border>
  </Panel>
</Window>