:root {
      --ink: #1d1d1f;
      --gray: #6e6e73;
      --gray-light: #d2d2d7;
      --card-bg: #fbfbfd;
      --white: #ffffff;
      --sans: -apple-system, "system-ui", "SF Pro Display", "SF Pro Text", "Segoe UI", Roboto, sans-serif;
      --max-w: 980px;
      --gap: 24px;
      --radius: 12px;
    }

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

    html, body {
      font-family: var(--sans);
      background-color: var(--white);
      color: var(--ink);
    }

    /* Navigation — mobile-first */
    nav {
      position: fixed;
      top: 0; left: 0; right: 0;
      height: 49px;
      background: rgba(255,255,255,0.8);
      backdrop-filter: blur(24px);
      border-bottom: 1px solid var(--gray-light);
      z-index: 1000;
    }

    .nav-content {
      max-width: var(--max-w);
      margin: 0 auto;
      padding: 0 var(--gap);
      height: 100%;
      display: flex;
      align-items: center;
      justify-content: space-between;
    }

    .nav-logo {
      font-size: 17px;
      font-weight: 600;
      text-decoration: none;
      color: var(--ink);
      letter-spacing: -0.3px;
    }

    .nav-hamburger {
      display: block;
      background: none;
      border: none;
      cursor: pointer;
      padding: 4px;
      color: var(--ink);
    }

    .nav-hamburger svg {
      width: 22px;
      height: 22px;
    }

    .nav-links {
      display: none;
      position: absolute;
      top: 49px; left: 0; right: 0;
      background: rgba(255,255,255,0.95);
      backdrop-filter: blur(20px);
      flex-direction: column;
      padding: 16px var(--gap) 24px;
      gap: 0;
      list-style: none;
      border-bottom: 1px solid var(--gray-light);
    }

    .nav-links.open { display: flex; }

    .nav-links li {
      padding-top: 12px; padding-bottom: 12px;
      border-bottom: 1px solid rgba(0,0,0,0.04);
    }

    .nav-links li:last-child {
      border-bottom: none;
      padding-top: 16px;
    }

    .nav-links a {
      font-size: 16px;
      font-weight: 400;
      color: var(--gray);
      text-decoration: none;
      transition: opacity 0.3s cubic-bezier(0.4,0,0.2,1);
    }

    .nav-links a:hover { opacity: 0.7; }

    /* Main content */
    main {
      padding-top: 49px;
      min-height: 100vh;
    }

    .container {
      max-width: var(--max-w);
      margin: 0 auto;
      padding: 0 var(--gap);
    }

    /* Hero section */
    .book-hero {
      display: grid;
      grid-template-columns: 320px 1fr;
      gap: 64px;
      align-items: start;
      padding: 80px 0 60px 0;
    }

    .book-cover {
      position: sticky;
      top: 80px;
    }

    .book-cover img {
      width: 100%;
      border-radius: 8px;
      box-shadow: 0 20px 60px rgba(0,0,0,0.12), 0 4px 20px rgba(0,0,0,0.08);
    }

    .book-info h1 {
      font-size: 42px;
      font-weight: 600;
      line-height: 1.15;
      letter-spacing: -0.5px;
      margin-bottom: 8px;
    }

    .book-subtitle {
      font-size: 18px;
      color: var(--gray);
      margin-bottom: 32px;
      line-height: 1.5;
    }

    .book-quote {
      font-size: 16px;
      font-style: italic;
      color: var(--gray);
      line-height: 1.7;
      padding: 24px 0;
      border-top: 1px solid var(--gray-light);
      border-bottom: 1px solid var(--gray-light);
      margin-bottom: 32px;
    }

    .book-meta {
      font-size: 14px;
      color: var(--gray);
      line-height: 1.8;
      margin-bottom: 32px;
    }

    .book-meta span {
      display: block;
    }

    .buy-btn {
      display: inline-block;
      background: var(--ink);
      color: var(--white);
      padding: 14px 36px;
      border-radius: 8px;
      text-decoration: none;
      font-size: 16px;
      font-weight: 500;
      transition: opacity 0.2s;
      letter-spacing: -0.2px;
    }

    .buy-btn:hover { opacity: 0.85; }

    /* Mockups gallery */
    .mockups-section {
      padding: 60px 0;
      overflow: hidden;
    }

    .mockups-grid {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 24px;
      max-width: 720px;
      margin: 0 auto;
    }

    .mockups-grid img {
      width: 100%;
      border-radius: 12px;
      object-fit: cover;
      aspect-ratio: 4/3;
    }

    @media (max-width: 480px) {
      .mockups-grid {
        grid-template-columns: 1fr;
      }
    }

    /* Divider */
    .section-divider {
      height: 1px;
      background-color: var(--gray-light);
      margin: 0;
    }

    /* TOC Section */
    .toc-section {
      max-width: 720px;
      margin: 0 auto;
      padding: 80px 0;
    }

    .toc-section h2 {
      font-size: 28px;
      font-weight: 600;
      letter-spacing: -0.3px;
      margin-bottom: 40px;
    }

    .toc-list {
      list-style: none;
    }

    .toc-list li {
      font-size: 17px;
      line-height: 1.6;
      padding: 10px 0;
      border-bottom: 1px solid rgba(0,0,0,0.04);
      color: var(--ink);
    }

    .toc-list li .ch-num {
      display: inline-block;
      width: 32px;
      color: var(--gray);
      font-size: 14px;
      font-weight: 500;
    }

    .toc-appendix {
      margin-top: 24px;
      padding-top: 24px;
      border-top: 1px solid var(--gray-light);
    }

    .toc-appendix li {
      font-size: 15px;
      color: var(--gray);
      border-bottom: none !important;
      padding: 6px 0;
    }

    /* Prolog section */
    .prolog-section {
      max-width: 720px;
      margin: 0 auto;
      padding: 80px 0;
    }

    .prolog-section h2 {
      font-size: 28px;
      font-weight: 600;
      letter-spacing: -0.3px;
      margin-bottom: 40px;
    }

    .prolog-section p {
      font-size: 17px;
      line-height: 1.8;
      color: var(--ink);
      margin-bottom: 20px;
    }

    .read-more-note {
      font-size: 15px;
      color: var(--gray);
      font-style: italic;
      margin-top: 32px;
      padding-top: 24px;
      border-top: 1px solid var(--gray-light);
    }

    /* CTA bottom */
    .cta-bottom {
      background: var(--card-bg);
      border-top: 1px solid var(--gray-light);
      border-bottom: 1px solid var(--gray-light);
      padding: 60px var(--gap);
      text-align: center;
      margin-bottom: 0;
    }

    .cta-bottom h2 {
      font-size: 24px;
      font-weight: 600;
      margin-bottom: 12px;
      letter-spacing: -0.3px;
    }

    .cta-bottom p {
      font-size: 16px;
      color: var(--gray);
      margin-bottom: 28px;
      line-height: 1.6;
    }

    .cta-links {
      display: flex;
      justify-content: center;
      gap: 16px;
      margin-top: 24px;
      flex-wrap: wrap;
    }

    .cta-links a {
      font-size: 14px;
      color: var(--gray);
      text-decoration: none;
      transition: color 0.2s;
    }

    .cta-links a:hover { color: var(--ink); }

    /* Footer */
    footer {
      background-color: var(--card-bg);
      border-top: 1px solid var(--gray-light);
      padding: 48px var(--gap);
      margin-top: 0;
    }

    .footer-content {
      max-width: var(--max-w);
      margin: 0 auto;
      display: flex;
      justify-content: space-between;
      align-items: center;
      font-size: 14px;
      color: var(--gray);
    }

    .footer-links {
      display: flex;
      list-style: none;
      gap: 32px;
    }

    .footer-links a {
      color: var(--gray);
      text-decoration: none;
      transition: color 0.2s;
    }

    .footer-links a:hover { color: var(--ink); }

    /* Responsive */
    @media (max-width: 768px) {
      body { overflow-x: hidden; }
      .container { padding: 0 20px; }
      .book-hero { grid-template-columns: 1fr; gap: 32px; padding: 48px 0 32px; }
      .book-cover { position: static; max-width: 240px; margin: 0 auto; }
      .book-info h1 { font-size: 28px; }
      .toc-section { padding: 48px 0; }
      .footer-content { flex-direction: column; gap: 16px; text-align: center; }
      .footer-links { gap: 16px; }
    }

    @media (min-width: 769px) {
      .nav-hamburger { display: none; }
      .nav-links {
        display: flex;
        position: static;
        background: none;
        backdrop-filter: none;
        flex-direction: row;
        padding: 0;
        gap: 32px;
        border-bottom: none;
      }
      .nav-links li {
        padding: 0;
        border-bottom: none;
      }
      .nav-links li:last-child { padding-top: 0; }
      .nav-links a { font-size: 12px; }
    }

    a:focus-visible, button:focus-visible { outline: 2px solid #1d1d1f; outline-offset: 2px; }