* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}
body {
    margin: 0;
    padding: 0;
    font-family: Arial, sans-serif;

    height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;

    background: linear-gradient(135deg, #ff9a9e, #fad0c4);
}

.login-box {
    background: white;
    padding: 30px;
    border-radius: 15px;
    width: 300px;

    box-shadow: 0 8px 20px rgba(0,0,0,0.2);
    text-align: center;
}

.login-box h2 {
    margin-bottom: 20px;
}

.login-box input {
    width: 100%;
    padding: 10px;
    margin: 10px 0;

    border: 1px solid #ccc;
    border-radius: 8px;
    outline: none;
}

.login-box input:focus {
    border-color: #ff6b6b;
}

.login-box button {
    width: 100%;
    padding: 10px;
    margin-top: 10px;

    background: #ff6b6b;
    color: white;
    border: none;
    border-radius: 8px;

    cursor: pointer;
    transition: 0.3s;
}

.login-box button:hover {
    background: #ff4d4d;
}

.error {
    color: red;
    font-size: 14px;
}
.back-btn {
    display: inline-block;
    margin-top: 15px;
    text-decoration: none;

    background: #555;
    color: white;
    padding: 8px 12px;
    border-radius: 8px;

    font-size: 14px;
    transition: 0.3s;
}

.back-btn:hover {
    background: #333;
    transform: scale(1.05);
}
/* ===== RESPONSIVE MOBILE LOGIN ===== */
@media (max-width: 768px) {
    body {
        padding: 20px;
        height: auto;
        min-height: 100vh;
    }

    .login-box {
        width: 100%;
        max-width: 360px;
        padding: 25px;
    }

    .login-box h2 {
        font-size: 22px;
    }

    .login-box input {
        font-size: 16px;
        padding: 12px;
    }

    .login-box button {
        font-size: 16px;
        padding: 12px;
    }

    .back-btn {
        font-size: 15px;
        padding: 10px 14px;
    }
}

/* ===== MOBILE NHỎ (IPHONE SE...) ===== */
@media (max-width: 480px) {
    .login-box {
        padding: 22px;
    }

    .login-box h2 {
        font-size: 20px;
    }
}