lab1/MainWindow.axaml

<Window 
    xmlns="https://github.com/avaloniaui"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d" 
    d:DesignWidth="800" 
    d:DesignHeight="450"
    x:Class="App.MainWindow"
    Title="AvaloniaFirst"
>
    Welcome to Avalonia!
</Window>