:root {
  --ink: #18242a;
  --muted: #647078;
  --paper: #fbf8f2;
  --surface: #ffffff;
  --teal: #0d7772;
  --coral: #d95f4b;
  --gold: #d7a23f;
  --line: rgba(24, 36, 42, 0.14);
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  color: var(--ink);
  background: var(--paper);
}

a {
  color: inherit;
}

.topbar {
  position: sticky;
  top: 0;
  z-index: 20;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 0.85rem clamp(1rem, 4vw, 3rem);
  background: rgba(251, 248, 242, 0.9);
  border-bottom: 1px solid var(--line);
  backdrop-filter: blur(16px);
}

.brand {
  font-weight: 800;
  text-decoration: none;
}

nav {
  display: flex;
  gap: clamp(0.6rem, 2vw, 1.5rem);
  font-size: 0.95rem;
}

nav a {
  color: var(--muted);
  text-decoration: none;
}

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

.hero {
  min-height: calc(100vh - 58px);
  display: grid;
  grid-template-columns: minmax(0, 0.9fr) minmax(320px, 1.1fr);
  align-items: center;
  gap: clamp(2rem, 5vw, 5rem);
  padding: clamp(2rem, 6vw, 5rem);
}

.hero-copy {
  max-width: 43rem;
}

.kicker {
  margin: 0 0 0.75rem;
  color: var(--teal);
  font-size: 0.78rem;
  font-weight: 850;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

h1,
h2,
h3,
p {
  text-wrap: pretty;
}

h1 {
  margin: 0;
  font-size: clamp(2.8rem, 7vw, 5.7rem);
  line-height: 1.02;
  letter-spacing: 0;
}

.lede {
  max-width: 38rem;
  margin: 1.4rem 0 0;
  color: #334047;
  font-size: clamp(1.08rem, 2vw, 1.28rem);
  line-height: 1.75;
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.8rem;
  margin-top: 2rem;
}

.primary,
.secondary {
  min-height: 44px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 0.82rem 1.1rem;
  border-radius: 8px;
  font-weight: 750;
  text-decoration: none;
}

.primary {
  color: white;
  background: var(--ink);
}

.secondary {
  color: var(--ink);
  border: 1px solid var(--line);
  background: rgba(255, 255, 255, 0.54);
}

.hero-media {
  margin: 0;
}

.hero-media img {
  width: 100%;
  display: block;
  border-radius: 8px;
  box-shadow: 0 24px 70px rgba(24, 36, 42, 0.18);
}

.book-strip {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  border-block: 1px solid var(--line);
  background: var(--surface);
}

.book-strip div {
  min-height: 96px;
  padding: 1.25rem clamp(1rem, 3vw, 2rem);
  border-right: 1px solid var(--line);
}

.book-strip div:last-child {
  border-right: 0;
}

.book-strip span {
  display: block;
  margin-bottom: 0.5rem;
  color: var(--muted);
  font-size: 0.82rem;
}

.book-strip strong {
  font-size: 1.05rem;
}

.section {
  padding: clamp(3.5rem, 8vw, 6.5rem) clamp(1rem, 5vw, 4rem);
}

.section-head {
  max-width: 58rem;
  margin-bottom: clamp(1.8rem, 4vw, 3rem);
}

.section h2 {
  margin: 0;
  font-size: clamp(2rem, 4.2vw, 3.4rem);
  line-height: 1.12;
}

.timeline {
  display: grid;
  grid-template-columns: repeat(5, minmax(0, 1fr));
  gap: 1px;
  background: var(--line);
  border: 1px solid var(--line);
}

.timeline article,
.model-cards article,
.question-grid article {
  background: var(--surface);
}

.timeline article {
  min-height: 270px;
  padding: 1.4rem;
}

.timeline span {
  color: var(--coral);
  font-weight: 850;
}

.timeline h3,
.model-cards h3,
.question-grid h3 {
  margin: 1rem 0 0.7rem;
  font-size: 1.2rem;
}

.timeline p,
.model-cards p,
footer p {
  margin: 0;
  color: var(--muted);
  line-height: 1.75;
}

.model-section {
  background: #eaf3f0;
}

.model-grid {
  display: grid;
  grid-template-columns: minmax(320px, 0.9fr) minmax(0, 1fr);
  gap: clamp(2rem, 5vw, 4rem);
  align-items: center;
}

.venn {
  position: relative;
  aspect-ratio: 1;
  min-height: 340px;
}

.circle {
  position: absolute;
  width: 62%;
  aspect-ratio: 1;
  display: grid;
  place-items: center;
  border-radius: 50%;
  color: white;
  font-size: clamp(1.4rem, 4vw, 2.4rem);
  font-weight: 850;
  mix-blend-mode: multiply;
}

.value {
  top: 0;
  left: 19%;
  background: rgba(13, 119, 114, 0.82);
}

.strength {
  bottom: 4%;
  left: 3%;
  background: rgba(217, 95, 75, 0.82);
}

.passion {
  right: 3%;
  bottom: 4%;
  background: rgba(215, 162, 63, 0.86);
}

.center {
  position: absolute;
  inset: 45% auto auto 50%;
  transform: translate(-50%, -50%);
  width: 9rem;
  height: 9rem;
  display: grid;
  place-items: center;
  border-radius: 50%;
  color: white;
  background: var(--ink);
  font-weight: 900;
  text-align: center;
  box-shadow: 0 16px 40px rgba(24, 36, 42, 0.22);
}

.model-cards,
.question-grid {
  display: grid;
  gap: 1rem;
}

.model-cards article,
.question-grid article {
  padding: 1.35rem;
  border: 1px solid var(--line);
  border-radius: 8px;
}

.questions-section {
  background: var(--surface);
}

.question-grid {
  grid-template-columns: repeat(3, 1fr);
}

ul {
  margin: 0.9rem 0 0;
  padding-left: 1.1rem;
  color: #36464d;
  line-height: 1.8;
}

.action-panel {
  display: grid;
  grid-template-columns: minmax(220px, 0.55fr) minmax(0, 1fr);
  gap: clamp(2rem, 5vw, 4rem);
  padding: clamp(1.5rem, 4vw, 3rem);
  color: white;
  background: var(--ink);
  border-radius: 8px;
}

.action-panel .kicker {
  color: #8dd4ca;
}

.action-panel h2 {
  color: white;
}

.action-panel ol {
  margin: 0;
  padding-left: 1.3rem;
  line-height: 1.9;
}

footer {
  padding: 2rem clamp(1rem, 5vw, 4rem);
  border-top: 1px solid var(--line);
  background: var(--surface);
}

@media (max-width: 920px) {
  .hero,
  .model-grid,
  .action-panel {
    grid-template-columns: 1fr;
  }

  .book-strip,
  .question-grid {
    grid-template-columns: repeat(2, 1fr);
  }

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

  .timeline article {
    min-height: unset;
  }
}

@media (max-width: 620px) {
  .topbar {
    align-items: flex-start;
    flex-direction: column;
  }

  nav {
    width: 100%;
    justify-content: space-between;
  }

  .hero {
    padding-top: 2rem;
  }

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

  .book-strip div {
    border-right: 0;
    border-bottom: 1px solid var(--line);
  }

  .book-strip div:last-child {
    border-bottom: 0;
  }

  .venn {
    min-height: 300px;
  }
}