gff/MainWindow.xaml

<Window x:Class="IS31Nabievv.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:IS31Nabievv"
        mc:Ignorable="d"
        Title="MainWindow" Height="450" Width="800">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="42*"/>
            <RowDefinition Height="341*"/>
            <RowDefinition Height="42*"/>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="159*"/>
            <ColumnDefinition Width="481*"/>
            <ColumnDefinition Width="152*"/>
        </Grid.ColumnDefinitions>
        <Rectangle Fill="#FFF4F4F5" HorizontalAlignment="Left" Height="42" Grid.Row="2" StrokeThickness="0"  Stroke="Black" VerticalAlignment="Top" Width="792" Grid.ColumnSpan="3"/>
        <Button Content="Назад" HorizontalAlignment="Left" Margin="10,11,0,0" VerticalAlignment="Top" Width="75" Click="ButtonBack_OnClick" x:Name="ButtonBack"/>
        <Frame Content="" Name="MainFrame" Source="Pages/AuthPage.xaml" HorizontalAlignment="Left" Height="336" Grid.Row="1" Navigated="MainFrame_OnNavigated" VerticalAlignment="Top" Width="792" Grid.ColumnSpan="3"/>

    </Grid>
</Window>