R29/WpfApp29/MainWindow.xaml

<Window x:Class="WpfApp29.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        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:local="clr-namespace:WpfApp29"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <Grid.Background>
            <ImageBrush ImageSource="/bg.png" Stretch="UniformToFill"/>
        </Grid.Background>

        <Border Padding="50" VerticalAlignment="Center" HorizontalAlignment="Center" Background="#E5ECCC74" BorderThickness="6" CornerRadius="30" BorderBrush="#FF312B04" Height="307" Grid.RowSpan="2">
            <Grid>

                <!--Надпись "Вход в личный кабинет"-->
                <Label Content="Вход в личный кабинет" HorizontalAlignment="Center" VerticalAlignment="Center" Margin="0, -200, 0, 0" FontSize="24" FontFamily="Copperplate Gothic Bold"></Label>

                <!--Поле для ввода логина-->
                <Label Content="Логин" HorizontalAlignment="Center" VerticalAlignment="Center" Margin="15, -100, 300, 0"></Label>
                <TextBox Name="TbLogin" Width="200" Height="40" HorizontalAlignment="Center" VerticalAlignment="Center" Margin="15, -100, 0, 0"
                         Text="{Binding User.Login}"></TextBox>

                <!--Поле для ввода пароля-->
                <Label Content="Пароль" HorizontalAlignment="Center" VerticalAlignment="Center" Margin="15, 25, 300, 0"></Label>
                <PasswordBox Name="TbPassword"  Width="200" Height="40" HorizontalAlignment="Center" VerticalAlignment="Center" Margin="15, 25, 0, 0"></PasswordBox>

                <!--Кнопка для входа в свой профиль-->
                <Button Width="150" Height="40" HorizontalAlignment="Center" VerticalAlignment="Center" 
                        Margin="-180, 150, 0, 0" Content="Зарегистрироваться" BorderBrush="#FF5A5205" 
                        Command="{Binding CommandGoRegister}"></Button>
                <Button Width="150" Height="40" HorizontalAlignment="Center" VerticalAlignment="Center" 
                        Margin="180, 150, 0, 0" Content="Войти" BorderBrush="#FF5A5205"  
                        Command="{Binding CommandLogin}" CommandParameter="{Binding ElementName=TbPassword}"></Button>

            </Grid>
        </Border>
    </Grid>
</Window>