AuthorizationKomadin/MainWindow.xaml

<Window x:Class="AuthorizationKomadin.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:AuthorizationKomadin"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid Margin="0,0,0,1">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*"/>
            <ColumnDefinition Width="295"/>
            <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"/>
            <RowDefinition Height="235"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <Rectangle Grid.ColumnSpan="3" Fill="#FFF4F4F5" Height="91" Stroke="Black" VerticalAlignment="Top" Grid.Row="2" StrokeThickness="0" />
        <Frame x:Name="MainFrame"  Grid.Row="1" Source="Pages/Page1.xaml"  Navigated="MainFrame_OnNavigated" Grid.ColumnSpan="3" Height="225" VerticalAlignment="Bottom" Margin="0,0,0,10" />
        <Button x:Name="ButtonBack" Content="Назад" HorizontalAlignment="Left" Margin="63,41,0,0" VerticalAlignment="Top" Width="61" Click="Button_Click_2"/>
    </Grid>
</Window>