:root {
  --bg: #000;
  --text: #f5f5f5;
  --muted: #bdbdbd;
  --line: #2a2a2a;
  --button: #e9e9e9;
  --button-text: #121212;
  --max: 1180px;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: "Poppins", "Segoe UI", Arial, Helvetica, sans-serif;
  line-height: 1.55;
}

a { color: inherit; }

.site-header {
  max-width: var(--max);
  margin: 0 auto;
  min-height: 112px;
  padding: 0 28px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  position: relative;
}

.brand {
  display: inline-flex;
  text-decoration: none;
  font-weight: 900;
  letter-spacing: .12em;
  font-size: 17px;
  align-items: center;
}

.brand-eki {
  background: #000;
  color: #fff;
  padding: 4px 2px 4px 5px;
}

.brand-lib {
  background: #fff;
  color: #000;
  padding: 4px 5px 4px 2px;
}

.menu-button {
  width: 56px;
  height: 46px;
  background: transparent;
  border: 0;
  cursor: pointer;
  display: grid;
  align-content: center;
  gap: 10px;
  padding: 8px;
  z-index: 20;
}

.menu-button span {
  display: block;
  height: 1px;
  width: 42px;
  background: #fff;
  transition: .25s ease;
}

.menu-button[aria-expanded="true"] span:first-child {
  transform: translateY(5.5px) rotate(45deg);
}

.menu-button[aria-expanded="true"] span:last-child {
  transform: translateY(-5.5px) rotate(-45deg);
}

.site-nav {
  position: absolute;
  z-index: 10;
  top: 86px;
  right: 28px;
  width: min(320px, calc(100vw - 56px));
  background: #101010;
  border: 1px solid #242424;
  padding: 12px;
  display: none;
}

.site-nav.open { display: grid; }

.site-nav a {
  text-decoration: none;
  padding: 14px 16px;
  border-bottom: 1px solid #242424;
}

.site-nav a:last-child { border-bottom: 0; }
.site-nav a:hover { background: #181818; }

.product-shell {
  max-width: var(--max);
  margin: 0 auto;
  padding: 46px 28px 84px;
}

.breadcrumb {
  font-size: 17px;
  margin-bottom: 48px;
  color: #efefef;
}

.breadcrumb span {
  padding: 0 10px;
  color: #8c8c8c;
}

.product-grid {
  display: grid;
  grid-template-columns: minmax(320px, 1fr) minmax(420px, .92fr);
  gap: 86px;
  align-items: start;
}

.book-column {
  display: flex;
  justify-content: center;
}

.book-cover {
  display: block;
  width: min(100%, 485px);
  height: auto;
}

.content-column h1 {
  margin: -7px 0 4px;
  font-size: clamp(38px, 4vw, 58px);
  line-height: 1.1;
  font-weight: 500;
  letter-spacing: -.03em;
}

.price {
  font-size: 28px;
  margin: 8px 0 30px;
}

.description {
  max-width: 670px;
  font-size: 21px;
}

.description p {
  margin: 0 0 22px;
}

.notice {
  margin-top: 56px;
  max-width: 690px;
}

.notice-heading {
  display: flex;
  align-items: center;
  gap: 16px;
}

.warning {
  font-size: 56px;
  line-height: 1;
}

.notice h2 {
  margin: 0;
  font-size: clamp(42px, 5vw, 64px);
  line-height: 1;
  font-weight: 700;
}

.notice p {
  font-size: 19px;
  font-weight: 700;
  margin: 22px 0 0;
}

.purchase-button {
  margin-top: 38px;
  width: 100%;
  min-height: 68px;
  border-radius: 999px;
  background: var(--button);
  color: var(--button-text);
  display: flex;
  align-items: center;
  justify-content: center;
  text-decoration: none;
  font-size: 19px;
  border: 1px solid #fff;
  transition: transform .15s ease, opacity .15s ease, background .15s ease;
}

.purchase-button:hover {
  transform: translateY(-1px);
  background: #fff;
}

.purchase-button.is-disabled {
  opacity: .65;
  cursor: not-allowed;
}

.checkout-note {
  color: #9b9b9b;
  font-size: 13px;
  text-align: center;
  margin: 14px 0 0;
}

.site-footer {
  max-width: var(--max);
  margin: 0 auto;
  padding: 34px 28px 50px;
  border-top: 1px solid var(--line);
  color: #bdbdbd;
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 18px 30px;
  font-size: 14px;
}

.site-footer strong { color: #fff; }
.site-footer p { margin: 7px 0 0; }

.footer-links {
  display: flex;
  flex-wrap: wrap;
  gap: 18px;
  justify-content: flex-end;
}

.footer-links a { text-decoration: none; }
.footer-links a:hover { color: #fff; }

.copyright {
  grid-column: 1 / -1;
  color: #767676;
}

.policy-page {
  max-width: 860px;
  margin: 0 auto;
  padding: 42px 28px 90px;
}

.policy-page h1 {
  font-size: clamp(36px, 6vw, 58px);
  margin: 0 0 12px;
}

.policy-page h2 {
  font-size: 24px;
  margin-top: 34px;
}

.policy-page p,
.policy-page li {
  color: #d4d4d4;
  font-size: 17px;
}

.policy-page a { color: #fff; }

.back-link {
  display: inline-block;
  margin-bottom: 34px;
  text-decoration: none;
  color: #aaa;
}

@media (max-width: 900px) {
  .site-header { min-height: 88px; }
  .product-shell { padding-top: 24px; }
  .breadcrumb { margin-bottom: 34px; }

  .product-grid {
    grid-template-columns: 1fr;
    gap: 48px;
  }

  .book-cover { width: min(88vw, 520px); }

  .content-column h1 {
    font-size: clamp(34px, 9vw, 48px);
  }

  .description { font-size: 18px; }
  .notice { margin-top: 44px; }
  .notice p { font-size: 17px; }

  .site-footer {
    grid-template-columns: 1fr;
  }

  .footer-links { justify-content: flex-start; }
}

@media (max-width: 520px) {
  .site-header,
  .product-shell,
  .site-footer,
  .policy-page {
    padding-left: 18px;
    padding-right: 18px;
  }

  .breadcrumb { font-size: 14px; }
  .price { font-size: 24px; }
  .warning { font-size: 42px; }
  .notice h2 { font-size: 44px; }
  .purchase-button { min-height: 60px; }
}