Session_2/Lopushok/UpdateCostWindow.xaml

<Window x:Class="Lopushok.UpdateCostWindow"
        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:Lopushok"
        mc:Ignorable="d"
        Title="Обновление стоимости" Height="250" Width="350" ResizeMode="NoResize" WindowStartupLocation="CenterScreen">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition/>
            <RowDefinition/>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition/>
            <ColumnDefinition/>
        </Grid.ColumnDefinitions>
        <TextBlock Style="{StaticResource DefaultTextBlock}">Стоимость:</TextBlock>
        <TextBox VerticalContentAlignment="Center" Style="{StaticResource DefaultTextBox}" Grid.Column="1" Name="TbCost"></TextBox>
        <Button Name="BtnUpdate" Click="BtnUpdate_Click" Grid.Row="1" Grid.Column="1" Style="{StaticResource DefaultButton}">Изменить</Button>
    </Grid>
</Window>