PM4/ych/LoginWindow.xaml

<Window x:Class="ych.LoginWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Вход в систему" Height="400" Width="400"
        WindowStartupLocation="CenterScreen" ResizeMode="NoResize" Background="#F4F6FA">

    <Grid>
        <Border VerticalAlignment="Top" Height="80" Background="#1F4E79">
            <TextBlock Text="Учёт оценок студентов" Foreground="White" FontSize="16"
                       FontWeight="Bold" FontFamily="Segoe UI"
                       HorizontalAlignment="Center" VerticalAlignment="Center"/>
        </Border>

        <StackPanel Margin="40,100,40,0">
            <!-- Поле Логин -->
            <TextBlock Text="Логин" FontFamily="Segoe UI" FontSize="12" Foreground="#555" Margin="0,0,0,4"/>
            <TextBox x:Name="LoginBox" FontFamily="Segoe UI" FontSize="13" Height="34" Padding="8,0"
                     Margin="0,0,0,14" BorderBrush="#C0CCE0" BorderThickness="1"/>

            <!-- Поле Пароль -->
            <TextBlock Text="Пароль" FontFamily="Segoe UI" FontSize="12" Foreground="#555" Margin="0,0,0,4"/>
            <PasswordBox x:Name="PassBox" FontFamily="Segoe UI" FontSize="13" Height="34" Padding="8,0"
                         Margin="0,0,0,20" BorderBrush="#C0CCE0" BorderThickness="1"/>

            <Button Content="Войти" Height="38" Background="#1F4E79" Foreground="White"
                    FontFamily="Segoe UI" FontSize="14" FontWeight="SemiBold" BorderThickness="0"
                    Cursor="Hand" Click="Button_Click"/>

            <TextBlock x:Name="ErrorText" Foreground="Red" FontFamily="Segoe UI" FontSize="12"
                       HorizontalAlignment="Center" Margin="0,10,0,0" Visibility="Collapsed"/>
        </StackPanel>
    </Grid>
</Window>