Slice/Cashier/MainWindow.xaml

<Window x:Class="Cashier.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:Cashier"
        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>
        <Grid>
            <Grid.ColumnDefinitions>
                <ColumnDefinition/>
                <ColumnDefinition/>
                <ColumnDefinition/>
            </Grid.ColumnDefinitions>
            <Button  Name="BtnStartWorkShift" Margin="50,17,50,20" Click="BtnStartWorkShift_Click">Начать смену</Button>
            <Button  Name="BtnBlockCashier" Grid.Column="1"  Margin="17" Click="BtnBlockCashier_Click">Заблокировать кассу</Button>
            <Button x:Name="BtnEndWorkShift" IsEnabled="False" Grid.Column="2" Content="Закончить смену"  Click="BtnEndWorkShift_Click"  Margin="47,17,47,17"></Button>
        </Grid>
        
        <Frame Grid.Row="1" Name="MainFrame" NavigationUIVisibility="Hidden" ContentRendered="MainFrame_ContentRendered"></Frame>
    </Grid>
</Window>