:root {
  --bg: #070b12;
  --ink: #111827;
  --muted: #5c6675;
  --paper: #f7f5f0;
  --white: #ffffff;
  --blue: #397bbd;
  --blue-dark: #245f9e;
  --orange: #c96a2d;
  --orange-bright: #e1833b;
  --line: rgba(255, 255, 255, 0.18);
  --shadow: 0 28px 70px rgba(0, 0, 0, 0.35);
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  color: var(--ink);
  background: var(--bg);
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  line-height: 1.65;
  text-rendering: optimizeLegibility;
}

img {
  display: block;
  max-width: 100%;
  height: auto;
}

.container {
  width: min(1120px, calc(100% - 40px));
  margin: 0 auto;
  position: relative;
  z-index: 1;
}

.narrow {
  width: min(920px, calc(100% - 40px));
}

.section {
  position: relative;
  overflow: hidden;
  padding: clamp(72px, 9vw, 140px) 0;
}

.section-dark {
  color: var(--white);
  background: #05070c url("../images/the-linear-trap-books.jpg") center / cover no-repeat fixed;
}

.overlay {
  position: absolute;
  inset: 0;
  background:
    radial-gradient(circle at 70% 10%, rgba(57, 123, 189, 0.35), transparent 34%),
    linear-gradient(180deg, rgba(0, 0, 0, 0.78), rgba(0, 0, 0, 0.86));
  z-index: 0;
}

.section-light {
  background: var(--paper);
}

h1,
h2,
h3 {
  margin: 0;
  line-height: 1.1;
  letter-spacing: -0.035em;
}

h1 {
  max-width: 900px;
  margin-bottom: 42px;
  font-size: clamp(2.35rem, 5.8vw, 5.25rem);
}

h2 {
  margin-bottom: 28px;
  font-size: clamp(2.1rem, 4.2vw, 4rem);
}

h3 {
  margin-top: 44px;
  margin-bottom: 10px;
  color: #e8edf6;
  font-size: clamp(1.05rem, 2vw, 1.35rem);
  text-transform: uppercase;
  letter-spacing: 0.08em;
}

p {
  margin: 0 0 1.25rem;
  font-size: clamp(1.05rem, 1.7vw, 1.32rem);
}

.hero p,
.contents-section p,
.contents-section li {
  color: rgba(255, 255, 255, 0.88);
}

.short-line {
  margin-bottom: 0.55rem;
}

.emphasis,
.equation,
.closing-question {
  color: var(--white);
  font-weight: 700;
}

.equation {
  margin: 0.85rem 0 1.9rem;
  padding: 22px 28px;
  border: 1px solid rgba(255, 255, 255, 0.22);
  border-left: 5px solid var(--blue);
  background: rgba(255, 255, 255, 0.07);
  font-size: clamp(1.35rem, 3vw, 2.45rem);
  font-style: italic;
  letter-spacing: -0.02em;
}

.closing-question {
  margin-top: 2rem;
  font-size: clamp(1.4rem, 2.7vw, 2.25rem);
  line-height: 1.28;
}

.book-grid {
  display: grid;
  grid-template-columns: minmax(240px, 390px) 1fr;
  gap: clamp(38px, 7vw, 88px);
  align-items: center;
}

.cover-wrap {
  justify-self: center;
}

.book-cover {
  width: min(390px, 100%);
  border-radius: 3px;
  box-shadow: var(--shadow);
}

.book-copy h2 {
  color: #111827;
}

.book-copy p {
  max-width: 720px;
  color: #263041;
}

.button-row {
  display: flex;
  flex-wrap: wrap;
  gap: 14px;
  margin-top: 34px;
}

.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 50px;
  padding: 14px 20px;
  border: 2px solid var(--blue);
  border-radius: 999px;
  color: var(--white);
  background: var(--blue);
  font-size: 1rem;
  font-weight: 800;
  line-height: 1;
  text-decoration: none;
  box-shadow: 0 12px 28px rgba(57, 123, 189, 0.24);
  transition: background-color 0.18s ease, border-color 0.18s ease, transform 0.18s ease, box-shadow 0.18s ease;
}

.button:hover,
.button:focus-visible {
  background: var(--blue-dark);
  border-color: var(--blue-dark);
  box-shadow: 0 16px 34px rgba(57, 123, 189, 0.32);
  transform: translateY(-1px);
}

.contents-section h2 {
  text-align: center;
}

.contents-list {
  max-width: 780px;
  margin: 0 auto;
}

.contents-list h3:first-child {
  margin-top: 0;
}

.contents-list ol {
  margin: 0 0 30px;
  padding-left: 1.4rem;
}

.contents-list li {
  margin-bottom: 20px;
  padding-left: 0.2rem;
  font-size: clamp(1rem, 1.45vw, 1.16rem);
}

.contents-list em {
  color: rgba(255, 255, 255, 0.72);
}

.footer {
  padding: 34px 0;
  color: rgba(255, 255, 255, 0.76);
  background: #05070c;
  text-align: center;
}

.footer p {
  margin: 0.15rem 0;
  font-size: 0.98rem;
}

.footer a {
  color: var(--orange-bright);
  font-weight: 700;
  text-decoration: none;
}

.footer a:hover,
.footer a:focus-visible {
  color: var(--orange);
  text-decoration: underline;
}

@media (max-width: 820px) {
  .section {
    padding: 66px 0;
  }

  .section-dark {
    background-attachment: scroll;
  }

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

  .book-copy {
    text-align: left;
  }

  .button-row {
    flex-direction: column;
    align-items: stretch;
  }

  .button {
    width: 100%;
  }
}

@media (max-width: 520px) {
  .container,
  .narrow {
    width: min(100% - 28px, 920px);
  }

  p {
    font-size: 1.03rem;
  }

  .equation {
    padding: 18px 20px;
  }
}