:root {
    --primary: #FFCB05;
    /* Vàng */
    --secondary: #00AEEF;
    /* Xanh */
    --accent: #F39C12;
    /* Cam */
    --danger: #FF5E5E;
    /* Đỏ */
    --success: #2ECC71;
    /* Xanh lá */
    --text: #333;
    --white: #fff;
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    font-family: 'Baloo 2', cursive;
    background-color: #f0f8ff;
    color: var(--text);
}

/* --- HEADER --- */
/* --- HEADER STYLES (Mặc định Desktop) --- */
header {
    background-color: var(--white);
    padding: 15px 30px;
    display: flex;
    justify-content: space-between;
    /* Đẩy logo sang trái, nút sang phải */
    align-items: center;
    box-shadow: 0 4px 10px rgba(0, 0, 0, 0.05);
    position: sticky;
    top: 0;
    z-index: 100;
    transition: all 0.3s ease;
}

.logo {
    font-size: 2rem;
    font-weight: 800;
    color: var(--secondary);
    display: flex;
    align-items: center;
    white-space: nowrap;
    /* Giữ logo không bị xuống dòng */
}

.logo span {
    color: var(--accent);
    margin-left: 5px;
}

.auth-buttons {
    display: flex;
    gap: 10px;
    /* Khoảng cách giữa 2 nút */
}

.auth-buttons button {
    border: none;
    padding: 10px 20px;
    border-radius: 25px;
    font-weight: bold;
    font-size: 1rem;
    cursor: pointer;
    font-family: inherit;
    transition: transform 0.2s;
    white-space: nowrap;
}

.btn-login {
    background-color: transparent;
    color: var(--secondary);
    border: 2px solid var(--secondary) !important;
}

.btn-register {
    background-color: var(--danger);
    color: var(--white);
    box-shadow: 0 4px 0 #c0392b;
}

.btn-register:active {
    transform: translateY(4px);
    box-shadow: none;
}

/* --- RESPONSIVE (Dành cho Mobile & Tablet) --- */
@media (max-width: 768px) {
    header {
        flex-direction: column;
        /* Xếp dọc: Logo trên, Nút dưới */
        padding: 15px;
        gap: 15px;
        /* Khoảng cách giữa Logo và cụm Nút */
    }

    .logo {
        font-size: 1.8rem;
        /* Giảm size logo một chút */
    }

    .auth-buttons {
        width: 100%;
        /* Cụm nút chiếm hết chiều ngang */
        justify-content: space-between;
        /* Chia đều không gian */
    }

    .auth-buttons button {
        flex: 1;
        /* Mỗi nút chiếm 50% diện tích để dễ bấm */
        padding: 12px 10px;
        /* Tăng vùng bấm (padding) */
        font-size: 0.95rem;
        display: flex;
        justify-content: center;
        align-items: center;
    }

    /* Ẩn chữ "Miễn Phí" để nút gọn hơn trên màn hình bé */
    .hide-on-mobile {
        display: none;
    }
}

/* --- HERO SECTION --- */
.hero {
    text-align: center;
    padding: 60px 20px;
    background: linear-gradient(180deg, #fff 0%, #f0f8ff 100%);
}

.hero h1 {
    font-size: 3rem;
    color: var(--secondary);
    margin-bottom: 10px;
}

.hero p {
    font-size: 1.2rem;
    color: #666;
    margin-bottom: 30px;
}

.hero-img-placeholder {
    width: 100%;
    max-width: 400px;
    height: 200px;
    background-color: #ddd;
    margin: 0 auto 30px;
    border-radius: 20px;
    display: flex;
    align-items: center;
    justify-content: center;
    color: #888;
}

/* --- SECTION TITLES --- */
.section-title {
    text-align: center;
    font-size: 2rem;
    margin: 40px 0 20px;
    color: var(--text);
}

/* --- CARD GRID --- */
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px 60px;
}

.grid {
    display: grid;
    /* Desktop: luôn 3 cột, dù có 1–2 quiz thì mỗi card vẫn chỉ chiếm 1/3 chiều ngang */
    grid-template-columns: repeat(3, minmax(0, 1fr));
    gap: 20px;
}

/* Tablet: 2 cột */
@media (max-width: 992px) {
    .grid {
        grid-template-columns: repeat(2, minmax(0, 1fr));
    }
}

/* Mobile: 1 cột */
@media (max-width: 576px) {
    .grid {
        grid-template-columns: 1fr;
    }
}



/* --- QUIZ CARD STYLES --- */
.card {
    background: var(--white);
    border-radius: 20px;
    padding: 20px;
    text-align: center;
    box-shadow: 0 5px 15px rgba(0, 0, 0, 0.05);
    transition: transform 0.3s;
    position: relative;
    overflow: hidden;
    border: 3px solid transparent;
}

.card:hover {
    transform: translateY(-5px);
    border-color: var(--primary);
}

.card-icon {
    font-size: 3rem;
    margin-bottom: 15px;
    display: block;
}

.card h3 {
    color: var(--secondary);
    margin-bottom: 10px;
}

.card p {
    color: #777;
    font-size: 0.9rem;
    margin-bottom: 20px;
}

.btn-start {
    background-color: var(--success);
    color: white;
    padding: 10px 25px;
    border-radius: 20px;
    text-decoration: none;
    font-weight: bold;
    display: inline-block;
}

/* --- MEMBER ONLY STYLES --- */
.card.locked {
    background-color: #f9f9f9;
    border: 2px dashed #ccc;
}

.card.locked .overlay {
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: rgba(255, 255, 255, 0.7);
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    backdrop-filter: blur(2px);
}

.lock-icon {
    font-size: 3rem;
    color: var(--danger);
    margin-bottom: 10px;
}

.btn-upgrade {
    background-color: var(--accent);
    color: white;
    padding: 8px 15px;
    border-radius: 15px;
    text-decoration: none;
    font-size: 0.9rem;
    font-weight: bold;
    box-shadow: 0 3px 0 #d35400;
    cursor: pointer;
}

/* --- FOOTER --- */
footer {
    background-color: var(--secondary);
    color: white;
    text-align: center;
    padding: 20px;
    margin-top: 50px;
}

/* --- USER PROFILE (HEADER) --- */
.user-profile {
    display: flex;
    align-items: center;
    gap: 15px;
}

.user-info {
    display: flex;
    align-items: center;
    gap: 8px;
    font-weight: bold;
    color: var(--secondary);
    background: #e1f5fe;
    padding: 5px 15px;
    border-radius: 20px;
}

.user-avatar {
    font-size: 1.5rem;
}

.btn-logout {
    background: transparent;
    border: 1px solid #ccc;
    padding: 5px 10px;
    border-radius: 10px;
    cursor: pointer;
    font-family: inherit;
    color: #666;
}

/* --- MODAL STYLES --- */
.modal-overlay {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: rgba(0, 0, 0, 0.5);
    z-index: 1000;
    display: none;
    /* Mặc định ẩn */
    align-items: center;
    justify-content: center;
    backdrop-filter: blur(3px);
}

.modal-overlay.open {
    display: flex;
}

.modal-box {
    background: white;
    width: 90%;
    max-width: 400px;
    padding: 30px;
    border-radius: 25px;
    box-shadow: 0 10px 25px rgba(0, 0, 0, 0.2);
    position: relative;
    animation: popIn 0.3s ease;
}

@keyframes popIn {
    from {
        transform: scale(0.8);
        opacity: 0;
    }

    to {
        transform: scale(1);
        opacity: 1;
    }
}

.close-btn {
    position: absolute;
    top: 10px;
    right: 15px;
    background: none;
    border: none;
    font-size: 2rem;
    color: #999;
    cursor: pointer;
}

/* Tabs */
.auth-tabs {
    display: flex;
    margin-bottom: 20px;
    border-bottom: 2px solid #eee;
}

.tab-btn {
    flex: 1;
    background: none;
    border: none;
    padding: 10px;
    font-family: inherit;
    font-weight: bold;
    font-size: 1.1rem;
    color: #999;
    cursor: pointer;
}

.tab-btn.active {
    color: var(--secondary);
    border-bottom: 3px solid var(--secondary);
}

/* Forms */
.input-group {
    margin-bottom: 15px;
    text-align: left;
}

.input-group label {
    display: block;
    margin-bottom: 5px;
    font-weight: bold;
    color: var(--text);
}

.input-group input {
    width: 100%;
    padding: 12px;
    border: 2px solid #eee;
    border-radius: 12px;
    font-family: inherit;
    font-size: 1rem;
    transition: border 0.2s;
}

.input-group input:focus {
    border-color: var(--secondary);
    outline: none;
}

.btn-submit {
    width: 100%;
    padding: 12px;
    background: var(--secondary);
    color: white;
    border: none;
    border-radius: 12px;
    font-weight: bold;
    font-size: 1.1rem;
    cursor: pointer;
    margin-top: 10px;
}

.btn-submit.register-color {
    background: var(--danger);
}

/* --- CARD UPDATES (AFTER LOGIN) --- */
/* Thêm Sao vàng khi hoàn thành */
.stars {
    color: #FFD700;
    margin-bottom: 5px;
    display: none;
    /* Mặc định ẩn */
}

.card.completed .stars {
    display: block;
}

.card.completed {
    border-color: var(--success);
}

/* Bỏ khóa */
.card.unlocked .overlay {
    display: none;
}

.card.unlocked {
    background: white;
    border: 2px solid var(--primary);
}

/* phụ huynh */
.btn-parent {
    background: var(--accent);
    border: none;
    padding: 6px 14px;
    border-radius: 12px;
    cursor: pointer;
    font-family: inherit;
    color: #fff;
    font-weight: bold;
    margin-right: 8px;
    box-shadow: 0 3px 0 #d35400;
}

.btn-parent:active {
    transform: translateY(2px);
    box-shadow: none;
}
.logo a {
    display: flex;
    align-items: center;
    color: inherit;
}

.logo-flag {
    width: 32px;      /* tùy chỉnh kích thước */
    height: 28px;
    margin-right: 8px;
    border-radius: 4px;  /* cho mềm góc, tùy thích */
    object-fit: cover;
}
/* FLASHCARD THUMBNAIL */
.flashcard-thumb {
    width: 100%;
    display: flex;
    align-items: center;
    justify-content: center;
    margin-bottom: 10px;
}

.flashcard-thumb img {
    max-height: 4.5rem;
    /* ≈ 1.5 lần card-icon 3rem */
    width: auto;
    object-fit: contain;
}