Slice/StoreServer/MainWindow.xaml

<Window x:Class="StoreServer.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:StoreServer"
        mc:Ignorable="d"
        Title="{Binding ElementName=MainFrame, Path=Content.Title}" Height="450" Width="800" WindowStartupLocation="CenterScreen" MinHeight="450" MinWidth="800">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="70"/>
            <RowDefinition/>
        </Grid.RowDefinitions>
        <Button x:Name="BtnBack" Content="Назад" HorizontalAlignment="Right" VerticalAlignment="Center" Width="100" Click="BtnBack_Click" Visibility="Collapsed" Height="30" Margin="0,0,20,0"></Button>
        <Frame Grid.Row="1" Name="MainFrame" NavigationUIVisibility="Hidden" ContentRendered="MainFrame_ContentRendered"></Frame>
    </Grid>
</Window>