School/SchoolProject/MainWindow.xaml

<Window x:Class="SchoolProject.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:SchoolProject"
        mc:Ignorable="d"
        Title="{Binding ElementName=MainFrame,Path=Content.Title}" Height="550" Width="1000" Style="{StaticResource MainWindow}" WindowStartupLocation="CenterScreen">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="40"/>
            <RowDefinition/>
        </Grid.RowDefinitions>

        <Button x:Name="BtnBack" Click="BtnBack_Click" HorizontalAlignment="Right" Margin="0,0,20,0">Назад</Button>
        <Frame Grid.Row="1" Name="MainFrame" NavigationUIVisibility="Hidden" ContentRendered="MainFrame_ContentRendered"></Frame>
    </Grid>
</Window>