avaloniaProject/Views/MainWindow.axaml

<Window xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:vm="using:avaloniaPr.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="avaloniaPr.Views.MainWindow"
        x:DataType="vm:MainWindowViewModel"
        Icon="/Assets/avalonia-logo.ico"
        Title="avaloniaPr">
	<Window.Styles>
		<Style Selector="TextBlock.TBLMain">
			<Setter Property="FontSize" Value="20"/>
			<Setter Property="Foreground" Value="Black"/>
		</Style>
		<Style Selector="TextBlock.centerTB">
			<Setter Property="FontSize" Value="30"/>
			<Setter Property="Foreground" Value="Black"/>
			<Setter Property="HorizontalAlignment" Value="Center"/>
			<Setter Property="VerticalAlignment" Value="Center"/>
			<Setter Property="FontWeight" Value="ExtraBold"/>
		</Style>
		<Style Selector="TextBox.TBMain">
			<Setter Property="FontSize" Value="15"/>
			<Setter Property="Margin" Value="0,20,0,0"/>
		</Style>
		<Style Selector="TextBox.TBCalculator">
			<Setter Property="FontSize" Value="30"/>
			<Setter Property="Margin" Value="10,20,10,20"/>
			<Setter Property="Width" Value="80"/>
			<Setter Property="Height" Value="80"/>
			<Setter Property="HorizontalContentAlignment" Value="Center"/>
			<Setter Property="VerticalContentAlignment" Value="Center"/>
		</Style>
		<Style Selector="TextBlock.TBLCalculator">
			<Setter Property="FontSize" Value="40"/>
			<Setter Property="Margin" Value="0,40,0,0"/>
			<Setter Property="Width" Value="80"/>
			<Setter Property="Height" Value="80"/>
			<Setter Property="TextAlignment" Value="Center"/>
		</Style>
		<Style Selector="Button.ButtonStyle">
			<Setter Property="FontSize" Value="20"/>
			<Setter Property="Width" Value="300"/>
			<Setter Property="Height" Value="40"/>
			<Setter Property="Margin" Value="0,20,0,0"/>
			<Setter Property="HorizontalContentAlignment" Value="Center"/>
			<Setter Property="Background" Value="#4c5866"/>
			<Setter Property="Foreground" Value="Black"/>
			<Setter Property="HorizontalAlignment" Value="Center"/>
			<Setter Property="VerticalAlignment" Value="Center"/>
		</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>
	<ContentControl Content="{Binding US}"></ContentControl>
</Window>