:root {
  --primary: #2f6f4f;
  --secondary: #7fbf6a;
  --bg: #f2f7e8;
  --accent: #f46f3a;
  --ink: #193024;
  --ink-soft: #375343;
  --paper: #fcfbf4;
  --radius: 24px;
  --turn-ms: 480ms;
}

*, *::before, *::after {
  box-sizing: border-box;
}

html, body {
  margin: 0;
  padding: 0;
  height: 100%;
  overflow: hidden;
  font-family: "Nunito", sans-serif;
  color: var(--ink);
  background:
    radial-gradient(ellipse at 20% 90%, rgba(127, 191, 106, 0.3), transparent 40%),
    radial-gradient(ellipse at 80% 10%, rgba(244, 111, 58, 0.12), transparent 30%),
    linear-gradient(180deg, #dbeec7 0%, #bfd8a0 40%, #8fbb7a 80%, #5a8f67 100%);
}

/* ===== Full-viewport book container ===== */
#book {
  position: fixed;
  inset: 0;
  left: clamp(48px, 6vw, 80px);
  right: clamp(48px, 6vw, 80px);
  display: grid;
  place-items: stretch;
}

/* ===== Page base ===== */
.page {
  grid-area: 1 / 1;
  display: flex;
  align-items: stretch;
  justify-content: stretch;
  padding: clamp(12px, 2vw, 24px);
  opacity: 1;
  transition: opacity 0.01s;
}

.page[hidden] {
  display: none;
}

/* Page surface */
.page-inner,
.cover-layout,
.credits-inner {
  flex: 1;
  display: flex;
  border-radius: var(--radius);
  background:
    radial-gradient(circle at top right, rgba(127, 191, 106, 0.06), transparent 30%),
    linear-gradient(180deg, #fffef7 0%, var(--paper) 100%);
  box-shadow:
    0 20px 50px rgba(25, 48, 36, 0.18),
    inset 0 0 0 1px rgba(47, 111, 79, 0.06);
  overflow: hidden;
}

/* ===== Cover ===== */
.cover-layout {
  display: grid;
  grid-template-columns: 1fr 1fr;
  align-items: center;
  gap: clamp(1rem, 3vw, 2.5rem);
  padding: clamp(1.5rem, 4vw, 3rem);
}

.cover-text {
  padding: 1rem;
}

.cover-eyebrow {
  margin: 0 0 0.4rem;
  font-size: 0.8rem;
  font-weight: 800;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--primary);
}

.cover-text h1 {
  margin: 0 0 0.6rem;
  font-family: "Baloo 2", cursive;
  font-size: clamp(2.2rem, 5vw, 4.5rem);
  line-height: 1;
  color: #113724;
}

.cover-subtitle {
  margin: 0 0 1.5rem;
  font-size: clamp(1rem, 2vw, 1.3rem);
  color: var(--ink-soft);
  line-height: 1.3;
}

.btn-start {
  display: inline-block;
  padding: 0.85rem 1.6rem;
  border: 0;
  border-radius: 999px;
  font: inherit;
  font-size: 1.1rem;
  font-weight: 800;
  color: #fff;
  background: linear-gradient(180deg, var(--accent), #d45c2c);
  box-shadow: 0 8px 20px rgba(212, 92, 44, 0.35);
  cursor: pointer;
  transition: transform 150ms ease, box-shadow 150ms ease;
}

.btn-start:hover,
.btn-start:focus-visible {
  transform: translateY(-2px);
  box-shadow: 0 12px 24px rgba(212, 92, 44, 0.4);
}

.btn-start:focus-visible {
  outline: 3px solid rgba(255, 217, 102, 0.9);
  outline-offset: 3px;
}

.cover-image {
  margin: 0;
  border-radius: 20px;
  overflow: hidden;
  box-shadow: 0 14px 36px rgba(25, 48, 36, 0.15);
}

.cover-image img {
  display: block;
  width: 100%;
  height: 100%;
  max-height: 60vh;
  object-fit: cover;
}

.cover-image figcaption {
  padding: 0.5rem 0.8rem;
  font-size: 0.78rem;
  color: var(--ink-soft);
  background: rgba(255, 255, 255, 0.8);
}

/* ===== Content pages ===== */
.page-inner {
  display: grid;
  padding: clamp(1rem, 2.5vw, 2rem);
  gap: clamp(0.8rem, 2vw, 1.5rem);
  align-items: center;
}

/* Layout variants */
.layout-hero-right .page-inner {
  grid-template-columns: minmax(0, 1fr) minmax(0, 1.2fr);
}

.layout-hero-left .page-inner {
  grid-template-columns: minmax(0, 1.2fr) minmax(0, 1fr);
}

.layout-split .page-inner {
  grid-template-columns: minmax(0, 1fr) minmax(0, 1.2fr);
}

.layout-climb .page-inner {
  grid-template-columns: minmax(0, 1.1fr) minmax(0, 0.9fr);
}

.layout-center .page-inner {
  grid-template-columns: 1fr;
  grid-template-rows: auto 1fr;
  justify-items: center;
  text-align: center;
}

/* ===== Story block ===== */
.story-block {
  padding: clamp(0.8rem, 2vw, 1.4rem);
  border-radius: 20px;
  background: rgba(252, 251, 244, 0.8);
  box-shadow: 0 6px 18px rgba(25, 48, 36, 0.06);
  align-self: center;
}

.page-text {
  margin: 0;
  font-size: clamp(1.2rem, 2.2vw, 1.8rem);
  font-weight: 700;
  line-height: 1.3;
}

.extras {
  margin: 0.8rem 0 0;
  padding: 0;
  list-style: none;
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.extras li {
  padding: 0.5rem 0.85rem;
  border-radius: 999px;
  font-size: 0.9rem;
  font-weight: 700;
  color: #154631;
  background: rgba(127, 191, 106, 0.2);
  border: 1px solid rgba(47, 111, 79, 0.12);
}

/* ===== Images ===== */
.page-image {
  margin: 0;
  border-radius: 18px;
  overflow: hidden;
  box-shadow: 0 10px 28px rgba(25, 48, 36, 0.12);
}

.page-image img {
  display: block;
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.page-image figcaption {
  padding: 0.4rem 0.7rem;
  font-size: 0.75rem;
  color: var(--ink-soft);
  background: rgba(255, 255, 255, 0.75);
}

.image-single {
  max-height: 70vh;
  align-self: center;
}

.image-single img {
  max-height: 60vh;
}

.image-wide img {
  aspect-ratio: 16 / 9;
}

/* Image pairs */
.image-pair {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: clamp(0.5rem, 1.5vw, 1rem);
  align-self: center;
}

.image-pair .page-image img {
  aspect-ratio: 4 / 3;
}

/* Decorative variants */
.hop-pair .page-image:first-child {
  transform: rotate(-2deg);
}
.hop-pair .page-image:last-child {
  transform: rotate(2deg);
}

.climb-pair {
  grid-template-columns: 1fr;
  grid-template-rows: 1fr 1fr;
  max-height: 100%;
}

.climb-pair .page-image {
  overflow: hidden;
}

.climb-pair .page-image img {
  aspect-ratio: 3 / 2;
  max-height: 35vh;
}

.compare-pair .page-image:first-child {
  background: rgba(175, 220, 206, 0.3);
}
.compare-pair .page-image:last-child {
  background: rgba(233, 239, 232, 0.5);
}

.contrast-pair .page-image:first-child {
  border: 3px solid rgba(244, 111, 58, 0.3);
}
.contrast-pair .page-image:last-child {
  border: 3px solid rgba(47, 111, 79, 0.2);
}

/* Ripple decoration */
.ripple-frame {
  position: relative;
}
.ripple-frame::before,
.ripple-frame::after {
  content: "";
  position: absolute;
  inset: -8px;
  border-radius: 24px;
  border: 2px solid rgba(47, 111, 79, 0.1);
  pointer-events: none;
}
.ripple-frame::after {
  inset: -18px;
  border-radius: 30px;
}

/* Water glow variant */
.water-glow {
  background: linear-gradient(180deg, rgba(175, 220, 206, 0.4), rgba(255, 255, 255, 0.6));
  padding: 6px;
}

/* ===== Credits page ===== */
.credits-inner {
  flex-direction: column;
  padding: clamp(1.2rem, 3vw, 2.5rem);
  overflow-y: auto;
}

.credits-inner h2 {
  margin: 0 0 1rem;
  font-family: "Baloo 2", cursive;
  font-size: clamp(1.6rem, 3vw, 2.4rem);
  color: #113724;
}

.credits-columns {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: clamp(1rem, 2vw, 2rem);
  flex: 1;
  min-height: 0;
}

.credits-columns section {
  padding: 1rem;
  border-radius: 16px;
  background: rgba(252, 251, 244, 0.6);
}

.credits-columns h3 {
  margin: 0 0 0.6rem;
  font-family: "Baloo 2", cursive;
  font-size: 1.3rem;
  color: #173e2a;
}

.source-list,
.credit-list {
  margin: 0;
  padding: 0 0 0 1rem;
  display: grid;
  gap: 0.6rem;
  font-size: 0.9rem;
}

.credit-list {
  padding-left: 0;
  list-style: none;
}

.source-list li,
.credit-list li {
  display: grid;
  gap: 0.15rem;
}

.source-list span,
.credit-list span {
  font-size: 0.82rem;
  color: var(--ink-soft);
}

.credits-inner a {
  color: var(--primary);
}

.credits-inner a:hover {
  color: #1b4a33;
}

/* ===== Navigation overlay buttons ===== */
.nav-btn {
  position: fixed;
  top: 50%;
  transform: translateY(-50%);
  z-index: 100;
  display: flex;
  align-items: center;
  justify-content: center;
  width: clamp(48px, 6vw, 72px);
  height: clamp(72px, 14vh, 120px);
  border: none;
  border-radius: 16px;
  background: rgba(25, 48, 36, 0.55);
  color: #fff;
  font-size: clamp(1.8rem, 3vw, 2.6rem);
  cursor: pointer;
  backdrop-filter: blur(4px);
  transition: background 150ms ease, transform 150ms ease, opacity 150ms ease;
  -webkit-tap-highlight-color: transparent;
}

.nav-btn:hover {
  background: rgba(25, 48, 36, 0.75);
}

.nav-btn:focus-visible {
  outline: 3px solid rgba(255, 217, 102, 0.9);
  outline-offset: 2px;
}

.nav-btn[disabled] {
  opacity: 0.25;
  cursor: default;
  pointer-events: none;
}

.nav-prev {
  left: 0;
}

.nav-next {
  right: 0;
}

.nav-arrow {
  display: block;
  line-height: 1;
  font-weight: 700;
}

/* ===== Page turn animations ===== */
.page.turn-out-forward {
  animation: turnOutFwd var(--turn-ms) ease-in forwards;
  z-index: 5;
}

.page.turn-in-forward {
  animation: turnInFwd var(--turn-ms) ease-out forwards;
  z-index: 4;
}

.page.turn-out-backward {
  animation: turnOutBack var(--turn-ms) ease-in forwards;
  z-index: 5;
}

.page.turn-in-backward {
  animation: turnInBack var(--turn-ms) ease-out forwards;
  z-index: 4;
}

@keyframes turnOutFwd {
  from { transform: perspective(1600px) rotateY(0deg); opacity: 1; }
  to   { transform: perspective(1600px) rotateY(-80deg); opacity: 0.2; }
}

@keyframes turnInFwd {
  from { transform: perspective(1600px) rotateY(80deg); opacity: 0.2; }
  to   { transform: perspective(1600px) rotateY(0deg); opacity: 1; }
}

@keyframes turnOutBack {
  from { transform: perspective(1600px) rotateY(0deg); opacity: 1; }
  to   { transform: perspective(1600px) rotateY(80deg); opacity: 0.2; }
}

@keyframes turnInBack {
  from { transform: perspective(1600px) rotateY(-80deg); opacity: 0.2; }
  to   { transform: perspective(1600px) rotateY(0deg); opacity: 1; }
}

/* ===== Responsive ===== */
@media (max-width: 768px) {
  #book {
    left: 40px;
    right: 40px;
  }

  .nav-btn {
    width: 36px;
    height: 64px;
    border-radius: 12px;
    font-size: 1.5rem;
  }

  .cover-layout {
    grid-template-columns: 1fr;
    grid-template-rows: auto 1fr;
    padding: 1.2rem;
    gap: 1rem;
  }

  .cover-text h1 {
    font-size: clamp(1.8rem, 8vw, 2.8rem);
  }

  .cover-image img {
    max-height: 35vh;
  }

  .layout-hero-right .page-inner,
  .layout-hero-left .page-inner,
  .layout-split .page-inner,
  .layout-climb .page-inner {
    grid-template-columns: 1fr;
    grid-template-rows: auto 1fr;
  }

  .image-pair {
    grid-template-columns: 1fr 1fr;
  }

  .climb-pair {
    grid-template-columns: 1fr 1fr;
    grid-template-rows: auto;
  }

  .image-single img {
    max-height: 40vh;
  }

  .hop-pair .page-image:first-child,
  .hop-pair .page-image:last-child {
    transform: none;
  }

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

@media (max-width: 480px) {
  .page {
    padding: 6px;
  }

  .page-inner {
    padding: 0.7rem;
    gap: 0.6rem;
  }

  .page-text {
    font-size: 1.1rem;
  }

  .extras li {
    font-size: 0.8rem;
    padding: 0.35rem 0.6rem;
  }

  .image-pair .page-image img {
    aspect-ratio: 1 / 1;
  }
}

/* ===== Reduced motion ===== */
@media (prefers-reduced-motion: reduce) {
  :root {
    --turn-ms: 1ms;
  }

  *, *::before, *::after {
    animation-duration: 1ms !important;
    transition-duration: 1ms !important;
  }
}