LanMountainDesktop/LanMountainDesktop.AirAppHost/AirAppWindow.axaml

<Window xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        x:Class="LanMountainDesktop.AirAppHost.AirAppWindow"
        Width="520"
        Height="360"
        MinWidth="360"
        MinHeight="260"
        WindowStartupLocation="CenterScreen"
        WindowDecorations="None"
        ExtendClientAreaToDecorationsHint="True"
        ExtendClientAreaTitleBarHeightHint="-1"
        TransparencyLevelHint="Transparent"
        Background="Transparent"
        FontFamily="{DynamicResource AppFontFamily}"
        Title="Air APP">
    <Border x:Name="WindowShell"
            Background="{DynamicResource AirAppWindowBackgroundBrush}"
            BorderBrush="{DynamicResource AirAppWindowBorderBrush}"
            BorderThickness="1"
            CornerRadius="18"
            ClipToBounds="True"
            BoxShadow="0 18 44 #22000000">
        <Grid RowDefinitions="52,*">
            <Grid x:Name="TitleBar"
                  ColumnDefinitions="*,Auto"
                  Background="Transparent"
                  PointerPressed="OnTitleBarPointerPressed">
                <StackPanel Margin="18,0,0,0"
                            VerticalAlignment="Center"
                            Spacing="2">
                    <TextBlock x:Name="TitleTextBlock"
                               Text="Air APP"
                               FontSize="15"
                               FontWeight="SemiBold"
                               Foreground="{DynamicResource AirAppTitleTextBrush}" />
                    <TextBlock x:Name="SubtitleTextBlock"
                               Text="LanMountainDesktop"
                               FontSize="11"
                               Foreground="{DynamicResource AirAppSecondaryTextBrush}" />
                </StackPanel>

                <Button Grid.Column="1"
                        Width="36"
                        Height="36"
                        Margin="0,8,10,8"
                        Padding="0"
                        Background="Transparent"
                        BorderBrush="Transparent"
                        BorderThickness="0"
                        Click="OnCloseClick">
                    <TextBlock Text="X"
                               FontSize="13"
                               FontWeight="SemiBold"
                               HorizontalAlignment="Center"
                               VerticalAlignment="Center"
                               Foreground="{DynamicResource AirAppTitleTextBrush}" />
                </Button>
            </Grid>

            <ContentControl x:Name="ContentHost"
                            Grid.Row="1" />
        </Grid>
    </Border>
</Window>