Slice/StoreServer/StartWorkPage.xaml

<Page x:Class="StoreServer.StartWorkPage"
      xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
      xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
      xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
      xmlns:local="clr-namespace:StoreServer"
      mc:Ignorable="d" 
      d:DesignHeight="450" d:DesignWidth="800"
      Title="Начало работы">

    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition/>
            <RowDefinition/>
        </Grid.RowDefinitions>
        <StackPanel Orientation="Horizontal" HorizontalAlignment="Center" VerticalAlignment="Bottom">
            <TextBlock Margin="0,0,20,0">Введите ID магазина:</TextBlock>
            <TextBox Width="80" Name="TxtIDStore" Margin="0,0,20,0"></TextBox>
            <Button x:Name="BtnFind" Content="Начать" Width="200" Click="BtnFind_Click"></Button>
        </StackPanel>
        <Button x:Name="BtnOfflineWork" Click="BtnOfflineWork_Click" Content="Работать оффлайн"  Grid.Row="1" HorizontalAlignment="Center" VerticalAlignment="Top" Margin="60" Height="40" Width="200"></Button>
    </Grid>
</Page>