---

```python
import sys

from PySide6.QtWidgets import (
    QApplication, QMainWindow, QWidget, QDialog,
    QLabel, QLineEdit, QPushButton, QVBoxLayout,
    QHBoxLayout, QScrollArea, QFrame, QMessageBox
)
from PySide6.QtCore import Qt


USERS = [
    {"login": "admin", "password": "1234", "full_name": "Администратор"}
]

PRODUCTS = [
    {
        "category": "Напитки",
        "name": "Вода",
        "description": "Питьевая вода",
        "manufacturer": "Аква",
        "supplier": "Поставщик 1",
        "price": 50.00,
        "unit": "шт.",
        "quantity": 20,
        "discount": 5
    },
    {
        "category": "Продукты",
        "name": "Шоколад",
        "description": "Молочный шоколад",
        "manufacturer": "Сладость",
        "supplier": "Поставщик 2",
        "price": 120.00,
        "unit": "шт.",
        "quantity": 0,
        "discount": 20
    },
    {
        "category": "Бытовая химия",
        "name": "Мыло",
        "description": "Мыло для рук",
        "manufacturer": "Чистота",
        "supplier": "Поставщик 3",
        "price": 80.00,
        "unit": "шт.",
        "quantity": 15,
        "discount": 18
    }
]


class LoginWindow(QDialog):
    def __init__(self):
        super().__init__()

        self.setWindowTitle("Авторизация")
        self.setFixedSize(340, 280)
        self.user = None

        layout = QVBoxLayout(self)
        layout.setSpacing(10)

        title = QLabel("Вход в систему")
        title.setAlignment(Qt.AlignmentFlag.AlignCenter)
        title.setStyleSheet("font-size: 20px; font-weight: bold;")
        layout.addWidget(title)

        layout.addWidget(QLabel("Логин"))
        self.login_entry = QLineEdit()
        self.login_entry.setPlaceholderText("Введите логин")
        layout.addWidget(self.login_entry)

        layout.addWidget(QLabel("Пароль"))
        self.password_entry = QLineEdit()
        self.password_entry.setPlaceholderText("Введите пароль")
        self.password_entry.setEchoMode(QLineEdit.EchoMode.Password)
        layout.addWidget(self.password_entry)

        login_button = QPushButton("Войти")
        login_button.clicked.connect(self.login)
        layout.addWidget(login_button)

        guest_button = QPushButton("Войти как гость")
        guest_button.clicked.connect(self.login_as_guest)
        layout.addWidget(guest_button)

        self.password_entry.returnPressed.connect(self.login)

    def login(self):
        login = self.login_entry.text().strip()
        password = self.password_entry.text()

        for user in USERS:
            if user["login"] == login and user["password"] == password:
                self.user = user["full_name"]
                self.accept()
                return

        QMessageBox.warning(
            self, "Ошибка входа", "Неверный логин или пароль"
        )

    def login_as_guest(self):
        self.user = "Гость"
        self.accept()


def get_background(product):
    if product["quantity"] == 0:
        return "#ADD8E6"
    if product["discount"] > 17:
        return "#FFDEAD"
    return "#FFFFFF"


class ProductsWindow(QMainWindow):
    def __init__(self, username):
        super().__init__()

        self.username = username
        self.setWindowTitle("Список товаров")
        self.resize(850, 600)

        central = QWidget()
        self.setCentralWidget(central)

        main_layout = QVBoxLayout(central)

        header = QHBoxLayout()

        title = QLabel("Список товаров")
        title.setStyleSheet("font-size: 22px; font-weight: bold;")
        header.addWidget(title)

        header.addStretch()

        user_label = QLabel(username)
        header.addWidget(user_label)

        logout_button = QPushButton("Выход")
        logout_button.clicked.connect(self.logout)
        header.addWidget(logout_button)

        main_layout.addLayout(header)

        self.scroll = QScrollArea()
        self.scroll.setWidgetResizable(True)

        self.list_widget = QWidget()
        self.list_layout = QVBoxLayout(self.list_widget)
        self.list_layout.setAlignment(Qt.AlignmentFlag.AlignTop)

        self.scroll.setWidget(self.list_widget)
        main_layout.addWidget(self.scroll)

        self.show_products()

    def show_products(self):
        for product in PRODUCTS:
            background = get_background(product)

            card = QFrame()
            card.setFrameShape(QFrame.Shape.Box)
            card.setStyleSheet(
                f"QFrame {{ background-color: {background}; "
                "border: 1px solid #555; }}"
            )

            card_layout = QHBoxLayout(card)

            info = QWidget()
            info_layout = QVBoxLayout(info)
            info_layout.setContentsMargins(5, 5, 5, 5)

            lines = [
                f'{product["category"]} | {product["name"]}',
                f'Описание: {product["description"]}',
                f'Производитель: {product["manufacturer"]}',
                f'Поставщик: {product["supplier"]}',
                f'Цена: {product["price"]:.2f}',
                f'Единица измерения: {product["unit"]}',
                f'Количество на складе: {product["quantity"]}'
            ]

            for index, text in enumerate(lines):
                label = QLabel(text)
                label.setWordWrap(True)

                if index == 0:
                    label.setStyleSheet(
                        "font-size: 14px; font-weight: bold; "
                        "border: none;"
                    )
                else:
                    label.setStyleSheet("border: none;")

                info_layout.addWidget(label)

            card_layout.addWidget(info, 1)

            discount = QLabel(f'{product["discount"]}%')
            discount.setAlignment(Qt.AlignmentFlag.AlignCenter)
            discount.setMinimumWidth(90)
            discount.setStyleSheet(
                "font-size: 22px; font-weight: bold; border: none;"
            )

            card_layout.addWidget(discount)
            self.list_layout.addWidget(card)

        self.list_layout.addStretch()

    def logout(self):
        self.close()


def main():
    app = QApplication(sys.argv)

    while True:
        login_window = LoginWindow()

        if login_window.exec() != QDialog.DialogCode.Accepted:
            break

        products_window = ProductsWindow(login_window.user)
        products_window.show()

        app.exec()

        # После закрытия списка возвращаемся к авторизации.
        # Закрытие главного приложения завершает программу.
        break


if __name__ == "__main__":
    main()
```