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

:root {
    --background: #f5f5f0;
    --surface: #ffffff;
    --text: #171717;
    --muted: #6b6b6b;
    --border: #deded8;
    --accent: #3157d5;
    --accent-dark: #2444ad;
}

html {
    scroll-behavior: smooth;
}

body {
    font-family: Arial, Helvetica, sans-serif;
    background: var(--background);
    color: var(--text);
    line-height: 1.6;
}

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

.container {
    width: min(1100px, calc(100% - 40px));
    margin: 0 auto;
}


/* =========================
   HEADER
========================= */

.header {
    height: 75px;
    border-bottom: 1px solid var(--border);
    background: rgba(245, 245, 240, 0.95);
}

.header-content {
    height: 100%;
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.logo {
    font-size: 20px;
    font-weight: 800;
    letter-spacing: -0.5px;
}

.nav {
    display: flex;
    gap: 30px;
}

.nav a {
    font-size: 14px;
    color: var(--muted);
    transition: color 0.2s ease;
}

.nav a:hover {
    color: var(--text);
}


/* =========================
   HERO
========================= */

.hero {
    padding: 110px 0 120px;
}

.hero-label,
.section-label {
    font-size: 12px;
    font-weight: 700;
    letter-spacing: 2px;
    color: var(--accent);
    margin-bottom: 18px;
}

.hero h1 {
    font-size: clamp(50px, 8vw, 90px);
    line-height: 0.95;
    letter-spacing: -5px;
    max-width: 850px;
    margin-bottom: 35px;
}

.hero h1 span {
    color: var(--accent);
}

.hero-description {
    max-width: 600px;
    font-size: 19px;
    color: var(--muted);
    margin-bottom: 35px;
}

.button {
    display: inline-block;
    background: var(--accent);
    color: white;
    padding: 14px 24px;
    border-radius: 6px;
    font-size: 14px;
    font-weight: 700;
    transition: background 0.2s ease, transform 0.2s ease;
}

.button:hover {
    background: var(--accent-dark);
    transform: translateY(-2px);
}


/* =========================
   CHAPTERS
========================= */

.chapters {
    padding: 100px 0;
    background: var(--surface);
}

.section-header {
    display: flex;
    justify-content: space-between;
    align-items: flex-end;
    gap: 40px;
    margin-bottom: 45px;
}

.section-header h2 {
    font-size: 48px;
    line-height: 1;
    letter-spacing: -2px;
}

.section-description {
    max-width: 350px;
    color: var(--muted);
    font-size: 15px;
}


/* =========================
   CHAPTER GRID
========================= */

.chapters-grid {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 15px;
}

.chapter {
    position: relative;
    display: grid;
    grid-template-columns: 60px 1fr 30px;
    gap: 20px;

    min-height: 190px;
    padding: 30px;

    border: 1px solid var(--border);
    background: var(--background);

    transition:
        transform 0.2s ease,
        border-color 0.2s ease,
        box-shadow 0.2s ease;
}

.chapter:hover {
    transform: translateY(-4px);
    border-color: var(--accent);
    box-shadow: 0 15px 35px rgba(0, 0, 0, 0.07);
}

.chapter-number {
    font-size: 13px;
    font-weight: 700;
    color: var(--accent);
}

.chapter-content h3 {
    font-size: 25px;
    line-height: 1.15;
    margin-bottom: 12px;
}

.chapter-content p {
    color: var(--muted);
    font-size: 14px;
    max-width: 350px;
}

.chapter-arrow {
    font-size: 24px;
    align-self: center;
    transition: transform 0.2s ease;
}

.chapter:hover .chapter-arrow {
    transform: translateX(5px);
}


/* =========================
   FOOTER
========================= */

.footer {
    padding: 30px 0;
    border-top: 1px solid var(--border);
    color: var(--muted);
    font-size: 13px;
}


/* =========================
   MOBILE
========================= */

@media (max-width: 700px) {

    .container {
        width: min(100% - 30px, 1100px);
    }

    .nav {
        display: none;
    }

    .hero {
        padding: 75px 0 85px;
    }

    .hero h1 {
        font-size: 52px;
        letter-spacing: -3px;
    }

    .hero-description {
        font-size: 17px;
    }

    .chapters {
        padding: 70px 0;
    }

    .section-header {
        display: block;
    }

    .section-header h2 {
        font-size: 40px;
        margin-bottom: 20px;
    }

    .chapters-grid {
        grid-template-columns: 1fr;
    }

    .chapter {
        grid-template-columns: 40px 1fr 20px;
        padding: 22px;
        min-height: 160px;
    }

    .chapter-content h3 {
        font-size: 21px;
    }

}