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

html {
    scroll-behavior: smooth;
}

body {
    font-family: Arial, sans-serif;
    background: #f4f8ff;
    color: #0f172a;
    line-height: 1.6;
}

a {
    text-decoration: none;
    color: inherit;
}

.container {
    width: min(1140px, calc(100% - 32px));
    margin: auto;
}

/* TOPBAR */
.topbar {
    background: rgba(255, 255, 255, 0.92);
    backdrop-filter: blur(10px);
    border-bottom: 1px solid #dbe4f0;
    padding: 14px 0;
    position: sticky;
    top: 0;
    z-index: 1000;
}

.topbar-wrap {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 16px;
    flex-wrap: wrap;
}

.home-btn {
    display: inline-block;
    padding: 10px 18px;
    border-radius: 999px;
    background: #0f172a;
    color: #ffffff;
    font-weight: 700;
    transition: 0.3s ease;
}

.home-btn:hover {
    transform: translateY(-2px);
    background: #1e293b;
}

.class-badge {
    padding: 8px 14px;
    border-radius: 999px;
    background: #dbeafe;
    color: #1e3a8a;
    font-weight: 700;
}

/* HERO */
.hero {
    padding: 34px 0 18px;
}

.hero-box {
    background: linear-gradient(135deg, #ffffff, #eef4ff);
    border: 1px solid #dbe4f0;
    border-radius: 30px;
    padding: 36px;
    box-shadow: 0 18px 40px rgba(15, 23, 42, 0.06);
}

.hero-label {
    display: inline-block;
    padding: 7px 13px;
    border-radius: 999px;
    background: #e0ecff;
    color: #1e40af;
    font-size: 0.85rem;
    font-weight: 700;
    margin-bottom: 14px;
}

.hero-box h1 {
    font-size: clamp(2rem, 4vw, 3rem);
    line-height: 1.15;
    margin-bottom: 12px;
}

.hero-box p {
    max-width: 720px;
    color: #475569;
}

/* SECTION */
.chapters-section {
    padding: 60px 0 70px;
}

.section-head {
    text-align: center;
    margin-bottom: 34px;
}

.mini-title {
    display: inline-block;
    color: #2563eb;
    text-transform: uppercase;
    letter-spacing: 0.08em;
    font-weight: 800;
    font-size: 0.84rem;
    margin-bottom: 10px;
}

.section-head h2 {
    font-size: clamp(1.8rem, 3vw, 2.5rem);
    margin-bottom: 8px;
}

.section-subtext {
    color: #64748b;
}

/* CHAPTER GRID */
.chapter-grid {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 22px;
}

.chapter-card {
    background: #ffffff;
    border: 1px solid #dbe4f0;
    border-radius: 24px;
    padding: 24px;
    box-shadow: 0 12px 28px rgba(15, 23, 42, 0.04);
    transition: 0.3s ease;
}

.chapter-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 18px 34px rgba(15, 23, 42, 0.08);
}

.chapter-number {
    width: 54px;
    height: 54px;
    border-radius: 16px;
    display: grid;
    place-items: center;
    background: linear-gradient(135deg, #dbeafe, #bfdbfe);
    color: #1e3a8a;
    font-weight: 800;
    margin-bottom: 14px;
}

.chapter-card h3 {
    font-size: 1.15rem;
    margin-bottom: 8px;
}

.chapter-card p {
    color: #475569;
    margin-bottom: 16px;
}

/* BUTTON GRID */
.button-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 12px;
}

.action-btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 100%;
    min-height: 48px;
    padding: 11px 14px;
    border-radius: 16px;
    font-size: 0.92rem;
    font-weight: 700;
    text-align: center;
    transition: all 0.3s ease;
    box-shadow: 0 8px 18px rgba(15, 23, 42, 0.08);
}

.open-btn {
    background: #f8f6f2;
    color: #1d4ed8;
    border: 1px solid #d6dde8;
}

.open-btn:hover {
    transform: translateY(-2px);
    background: #eef4ff;
}

.download-btn-small {
    background: #081635;
    color: #ffffff;
    border: 1px solid #081635;
}

.download-btn-small:hover {
    transform: translateY(-2px);
    background: #102044;
}

/* FOOTER */
.footer {
    background: #0f172a;
    color: #e2e8f0;
    padding: 28px 0;
}

.footer-wrap {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 20px;
    flex-wrap: wrap;
}

.footer p {
    color: #cbd5e1;
    margin-top: 6px;
}

.footer-home {
    display: inline-block;
    padding: 10px 18px;
    border-radius: 999px;
    background: #2563eb;
    color: #ffffff;
    font-weight: 700;
    transition: 0.3s ease;
}

.footer-home:hover {
    transform: translateY(-2px);
}

/* RESPONSIVE */
@media (max-width: 860px) {
    .chapter-grid {
        grid-template-columns: 1fr;
    }
}

@media (max-width: 640px) {
    .hero-box,
    .chapter-card {
        padding: 20px;
    }

    .topbar-wrap,
    .footer-wrap {
        flex-direction: column;
        align-items: flex-start;
    }

    .button-grid {
        grid-template-columns: 1fr 1fr;
        gap: 10px;
    }

    .action-btn {
        min-height: 44px;
        font-size: 0.82rem;
        padding: 10px 10px;
    }
}