.gradient-background {
    background: linear-gradient(to right, #FFFFFF, #4A90E2, #000000);
    min-height: 100vh;
    width: 100%;
    position: absolute;
    top: 0;
    left: 0;
    z-index: -1;
    padding: 16px;
    display: flex;
    justify-content: center;
    align-items: center;
}

#login_screen, #register_screen {
    background: white;
    padding: 20px;
    border-radius: 8px;
    box-shadow: 0 0 10px rgba(0,0,0,0.1);
    text-align: center;
}

#login-form, #register-form {
    display: flex;
    flex-direction: column;
    gap: 10px;
    margin-bottom: 15px;
}

input, button {
    padding: 10px;
    font-size: 16px;
    border-radius: 5px;
}

input {
    border: 1px solid #ccc;
}

button {
    background: #007bff;
    color: white;
    border: none;
    cursor: pointer;
}

button:hover {
    background: #0056b3;
}

.auth-link {
    color: #007bff;
    font-weight: bold;
    text-decoration: underline;
    cursor: pointer;
}

.auth-link:hover {
    color: #0056b3;
}

nav {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    background: #333;
    color: white;
    padding: 10px;
    display: flex;
    justify-content: left;
    align-items: center;
}

nav ul {
    list-style: none;
    display: flex;
    gap: 20px;
    margin: 0;
    padding-left: 20px;
}

nav a {
    color: white;
    text-decoration: none;
}

.ad-banner {
    width: 200px;
    height: 100%;
    position: absolute;
    top: 60px;
}

.ad-banner.left {
    left: 0;
}

.ad-banner.right {
    right: 0;
}

.ad-banner img {
    width: 100%;
    height: auto;
}

.product-list {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 20px;
    margin: 80px 220px 20px 220px;
    padding: 20px;
}

.product {
    background: white;
    padding: 20px;
    border-radius: 8px;
    text-align: center;
    cursor: pointer;
}

.product img {
    width: 100%;
    height: auto;
}

.product-details {
    background: white;
    padding: 20px;
    border-radius: 8px;
    text-align: center;
    max-width: 600px;
    margin: 80px auto 20px auto;
}

.product-details img {
    width: 100%;
    height: auto;
    margin-bottom: 20px;
}

.reviews {
    margin-top: 20px;
    text-align: left;
}

.add-to-cart {
    background: #28a745;
    color: white;
    border: none;
    padding: 10px 20px;
    cursor: pointer;
    margin-top: 20px;
}

.add-to-cart:hover {
    background: #218838;
}

@media (max-width: 768px) {
    .product-list {
        grid-template-columns: 1fr;
        margin: 80px 20px 20px 20px;
    }

    .ad-banner {
        display: none;
    }

    .product-details {
        margin: 80px 20px 20px 20px;
    }

    nav ul {
        flex-direction: column;
        padding-left: 10px;
    }

    .login-btn {
        margin-right: 10px;
    }
}