AvaloniaCatBase/AvaloniaApplicationBase/Views/MainWindow.axaml

<Window xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:vm="using:AvaloniaApplicationBase.ViewModels"
        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="AvaloniaApplicationBase.Views.MainWindow"
        x:DataType="vm:MainWindowViewModel"
        Icon="/Assets/avalonia-logo.ico"
        Title="AvaloniaApplicationBase">
	<Window.Styles>
		<Style Selector="TextBlock">
			<Setter Property="FontSize" Value="28"></Setter>
		</Style>
		<Style Selector="Button">
			<Setter Property="Background" Value="Violet"/>
			<Setter Property="FontSize" Value="28"/>
			<Setter Property="FontWeight" Value="Bold"/>
		</Style>
	</Window.Styles>
    <Design.DataContext>
        <!-- This only sets the DataContext for the previewer in an IDE,
             to set the actual DataContext for runtime, set the DataContext property in code (look at App.axaml.cs) -->
        <vm:MainWindowViewModel/>
    </Design.DataContext>
	<Grid>
		<ContentControl Content="{Binding US}"></ContentControl>
	</Grid>
	
</Window>