Avalonia/AvaloniaApplication3/Views/StartWindow.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"
		xmlns:vm="using:AvaloniaApplication3.ViewModels"
        mc:Ignorable="d" d:DesignWidth="1440" d:DesignHeight="990"
        x:Class="AvaloniaApplication3.Views.StartWindow"
		x:DataType="vm:StartWindowViewModel"
		Icon="/Assets/avalonia-logo.ico"
        Title="StartWindow">
	<StackPanel>
		<UserControl Content="{Binding MainAcc}"/>
	</StackPanel>
</Window>