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.ColumnDefinitions>
            <ColumnDefinition/>
            <ColumnDefinition/>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition/>
            <RowDefinition/>
        </Grid.RowDefinitions>

        <TextBlock Margin="5" HorizontalAlignment="Right" VerticalAlignment="Bottom">ID магазина:</TextBlock>
        <Button Grid.Row="1" Grid.ColumnSpan="2" Height="30" x:Name="BtnFind" Content="Начать" Margin="300,20,300,0" VerticalAlignment="Top" Click="BtnFind_Click"></Button>
        <TextBox Grid.Column="1" Name="TxtIDStore" VerticalAlignment="Bottom"  Margin="7,0,250,7"/>


    </Grid>
</Page>