/* Reset cơ bản */
    * {
        margin: 0;
        padding: 0;
        box-sizing: border-box;
        font-family: "Poppins", sans-serif;
    }

    body {
        background: linear-gradient(to right, #e3f2fd, #ffffff);
        color: #333;
    }

    /* HEADER */
    header {
        background: linear-gradient(90deg, #004aad, #0077b6);
        color: white;
        padding: 20px 0;
        display: flex;
        align-items: center;
        justify-content: center;
        gap: 15px;
        box-shadow: 0 3px 10px rgba(0,0,0,0.2);
        position: sticky;
        top: 0;
        z-index: 1000;
    }

    header img {
        height: 60px;
    }

    header h1 {
        font-size: 26px;
        font-weight: 600;
        text-shadow: 1px 1px 3px rgba(0,0,0,0.3);
    }

    /* NAVIGATION */
    nav {
        background: #023e8a;
        text-align: center;
        padding: 10px 0;
        position: sticky;
        top: 90px;
        z-index: 999;
    }

    nav a {
        color: #fff;
        text-decoration: none;
        padding: 10px 18px;
        margin: 0 10px;
        border-radius: 6px;
        font-weight: 500;
        transition: 0.3s;
    }

    nav a:hover {
        background: #0077b6;
        transform: scale(1.1);
    }

    /* MAIN SECTION */
    .hero {
        background: url('https://images.unsplash.com/photo-1524995997946-a1c2e315a42f') center/cover no-repeat;
        height: 400px;
        display: flex;
        flex-direction: column;
        justify-content: center;
        align-items: center;
        color: white;
        text-shadow: 2px 2px 5px rgba(0,0,0,0.6);
    }

    .hero h2 {
        font-size: 40px;
        margin-bottom: 10px;
    }

    .hero p {
        font-size: 18px;
    }

    /* SEARCH BOX */
    .search-box {
        text-align: center;
        margin: 30px auto;
    }

    .search-box input {
        width: 60%;
        padding: 10px 15px;
        border: 2px solid #0077b6;
        border-radius: 25px;
        font-size: 16px;
        transition: 0.3s;
    }

    .search-box input:focus {
        outline: none;
        box-shadow: 0 0 10px #0077b6;
    }

    /* BOOK SECTION */
    .book-section {
        max-width: 1100px;
        margin: auto;
        background: white;
        padding: 30px;
        border-radius: 10px;
        box-shadow: 0 4px 15px rgba(0,0,0,0.1);
        margin-bottom: 50px;
    }

    .book-section h2 {
        text-align: center;
        color: #004aad;
        margin-bottom: 25px;
    }

    .book-list {
        display: flex;
        flex-wrap: wrap;
        justify-content: center;
        gap: 25px;
    }

    .book {
        width: 220px;
        background: #f8f9fa;
        border-radius: 10px;
        overflow: hidden;
        box-shadow: 0 3px 10px rgba(0,0,0,0.1);
        transition: transform 0.3s, box-shadow 0.3s;
    }

    .book:hover {
        transform: translateY(-8px);
        box-shadow: 0 8px 20px rgba(0,0,0,0.2);
    }

    .book img {
        width: 100%;
        height: 280px;
        object-fit: cover;
    }

    .book h3 {
        text-align: center;
        margin-top: 10px;
        color: #023e8a;
        font-size: 18px;
    }

    .book p {
        text-align: center;
        font-size: 14px;
        color: #555;
        padding: 5px 10px 15px;
    }

    /* FOOTER */
    footer {
        background: linear-gradient(90deg, #004aad, #0077b6);
        color: white;
        text-align: center;
        padding: 20px;
        font-size: 14px;
    }

    footer a {
        color: #90e0ef;
        text-decoration: none;
    }

    footer a:hover {
        text-decoration: underline;
    }

    /* RESPONSIVE */
    @media(max-width: 768px) {
        .book-list {
            flex-direction: column;
            align-items: center;
        }
        .search-box input {
            width: 90%;
        }
        header h1 {
            font-size: 20px;
        }
    }