:root {
  --page-width: 674px;
  --page-height: 952px;
  --book-width: 1366px;
  --book-gap: 18px;
  --ink: #f5f1e8;
  --accent: #c9ab64;
  --bg-deep: #071b1c;
  --bg: #0c2928;
  --control: rgba(9, 31, 31, 0.76);
  --control-hover: rgba(20, 56, 53, 0.94);
}

* { box-sizing: border-box; }

html,
body {
  width: 100%;
  height: 100%;
  margin: 0;
  overflow: hidden;
  background: var(--bg-deep);
}

body {
  color: var(--ink);
  font-family: Arial, "Helvetica Neue", sans-serif;
  -webkit-font-smoothing: antialiased;
  -webkit-tap-highlight-color: transparent;
  touch-action: none;
  user-select: none;
}

button { font: inherit; }

#app,
.book-stage {
  width: 100%;
  height: 100%;
}

.book-stage {
  position: relative;
  display: grid;
  place-items: center;
  overflow: hidden;
  isolation: isolate;
  background:
    radial-gradient(circle at 50% 44%, rgba(55, 105, 95, 0.34), transparent 42%),
    linear-gradient(145deg, var(--bg), var(--bg-deep) 72%);
}

.book-stage::after {
  content: "";
  position: absolute;
  inset: 0;
  z-index: -1;
  opacity: 0.16;
  pointer-events: none;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='140' height='140' viewBox='0 0 140 140'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='.72' numOctaves='2' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23n)' opacity='.18'/%3E%3C/svg%3E");
}

.book {
  position: relative;
  width: var(--book-width);
  height: var(--page-height);
  perspective: 2200px;
  filter: drop-shadow(0 22px 42px rgba(0, 0, 0, 0.43));
}

.spread-layer {
  position: absolute;
  inset: 0;
  display: grid;
  grid-template-columns: var(--page-width) var(--page-width);
  column-gap: var(--book-gap);
  transform-style: preserve-3d;
  backface-visibility: hidden;
  will-change: transform, opacity;
}

.spread-layer.current { z-index: 2; }
.spread-layer.incoming { z-index: 1; opacity: 0; pointer-events: none; }
.spread-layer.underlay { z-index: 1; opacity: 1; pointer-events: none; }
.spread-layer.mask-right .right-sheet,
.spread-layer.mask-left .left-sheet { visibility: hidden; }

.sheet {
  position: relative;
  width: var(--page-width);
  height: var(--page-height);
  margin: 0;
  overflow: hidden;
  background: #f8f6ef;
  box-shadow: inset 0 0 0 1px rgba(46, 40, 26, 0.08);
}

.left-sheet { border-radius: 5px 1px 1px 5px; }
.right-sheet { border-radius: 1px 5px 5px 1px; }

.sheet::after {
  content: "";
  position: absolute;
  inset: 0;
  pointer-events: none;
}

.left-sheet::after {
  background: linear-gradient(90deg, transparent 89%, rgba(18, 22, 19, 0.10));
}

.right-sheet::after {
  background: linear-gradient(270deg, transparent 89%, rgba(18, 22, 19, 0.10));
}

.sheet.is-blank {
  background:
    linear-gradient(90deg, rgba(0, 0, 0, 0.035), transparent 12%),
    #f5f1e7;
}

.sheet img {
  display: block;
  width: 100%;
  height: 100%;
  object-fit: contain;
  background: #fff;
  -webkit-user-drag: none;
}

.sheet.is-blank img { display: none; }

.book-fold {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 50%;
  z-index: 5;
  width: var(--book-gap);
  transform: translateX(-50%);
  pointer-events: none;
  background: linear-gradient(90deg, rgba(0, 0, 0, 0.22), rgba(255, 255, 255, 0.09) 46%, rgba(0, 0, 0, 0.19));
  box-shadow: 0 0 18px rgba(0, 0, 0, 0.26);
}

.flip-leaf {
  position: absolute;
  top: 0;
  z-index: 7;
  display: none;
  width: var(--page-width);
  height: var(--page-height);
  transform-style: preserve-3d;
  backface-visibility: hidden;
  will-change: transform, filter;
}

.flip-leaf.next {
  left: calc(var(--page-width) + var(--book-gap));
  display: block;
  transform-origin: left center;
}

.flip-leaf.previous {
  left: 0;
  display: block;
  transform-origin: right center;
}

.flip-face {
  position: absolute;
  inset: 0;
  overflow: hidden;
  background: #fff;
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
  box-shadow: inset 0 0 0 1px rgba(46, 40, 26, 0.08);
}

.flip-face img {
  display: block;
  width: 100%;
  height: 100%;
  object-fit: contain;
  background: #fff;
  -webkit-user-drag: none;
}

.flip-front { transform: translateZ(1px); }
.flip-back { transform: rotateY(180deg) translateZ(1px); }

.flip-front::after,
.flip-back::after {
  content: "";
  position: absolute;
  inset: 0;
  pointer-events: none;
}

.flip-leaf.next .flip-front::after,
.flip-leaf.previous .flip-back::after {
  background: linear-gradient(90deg, rgba(0, 0, 0, 0.22), transparent 16%);
}

.flip-leaf.next .flip-back::after,
.flip-leaf.previous .flip-front::after {
  background: linear-gradient(270deg, rgba(0, 0, 0, 0.22), transparent 16%);
}

.flip-leaf.next .flip-face { border-radius: 1px 5px 5px 1px; }
.flip-leaf.previous .flip-face { border-radius: 5px 1px 1px 5px; }

.book.turning-next .flip-leaf.next {
  animation: page-flip-next 820ms cubic-bezier(.30, .04, .20, 1) both;
}

.book.turning-previous .flip-leaf.previous {
  animation: page-flip-previous 820ms cubic-bezier(.30, .04, .20, 1) both;
}

@keyframes page-flip-next {
  0% {
    transform: rotateY(0deg) translateZ(0);
    filter: drop-shadow(0 8px 8px rgba(0, 0, 0, 0.08));
  }
  42% {
    transform: rotateY(-78deg) translateZ(12px);
    filter: drop-shadow(-24px 18px 20px rgba(0, 0, 0, 0.42));
  }
  58% {
    transform: rotateY(-104deg) translateZ(12px);
    filter: drop-shadow(-30px 18px 22px rgba(0, 0, 0, 0.44));
  }
  100% {
    transform: rotateY(-180deg) translateZ(0);
    filter: drop-shadow(0 8px 8px rgba(0, 0, 0, 0.08));
  }
}

@keyframes page-flip-previous {
  0% {
    transform: rotateY(0deg) translateZ(0);
    filter: drop-shadow(0 8px 8px rgba(0, 0, 0, 0.08));
  }
  42% {
    transform: rotateY(78deg) translateZ(12px);
    filter: drop-shadow(24px 18px 20px rgba(0, 0, 0, 0.42));
  }
  58% {
    transform: rotateY(104deg) translateZ(12px);
    filter: drop-shadow(30px 18px 22px rgba(0, 0, 0, 0.44));
  }
  100% {
    transform: rotateY(180deg) translateZ(0);
    filter: drop-shadow(0 8px 8px rgba(0, 0, 0, 0.08));
  }
}

.nav-button,
.fullscreen-button {
  border: 1px solid rgba(213, 193, 140, 0.30);
  color: var(--ink);
  background: var(--control);
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.24);
  cursor: pointer;
}

.nav-button {
  position: absolute;
  top: 50%;
  z-index: 10;
  display: grid;
  place-items: center;
  width: 64px;
  height: 64px;
  padding: 0;
  border-radius: 50%;
  transform: translateY(-50%);
  transition: background 150ms ease, border-color 150ms ease, opacity 150ms ease, transform 150ms ease;
}

.nav-button.previous { left: 24px; }
.nav-button.next { right: 24px; }

.nav-button svg,
.fullscreen-button svg {
  width: 28px;
  height: 28px;
  fill: none;
  stroke: currentColor;
  stroke-width: 1.8;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.nav-button:hover,
.nav-button:active,
.fullscreen-button:hover,
.fullscreen-button:active {
  background: var(--control-hover);
  border-color: rgba(213, 193, 140, 0.68);
}

.nav-button:active { transform: translateY(-50%) scale(0.96); }

.nav-button:disabled {
  opacity: 0.22;
  cursor: default;
}

.nav-button:focus-visible,
.fullscreen-button:focus-visible {
  outline: 3px solid var(--accent);
  outline-offset: 4px;
}

.control-dock {
  position: absolute;
  left: 50%;
  bottom: 11px;
  z-index: 11;
  display: flex;
  align-items: center;
  height: 44px;
  padding: 0 7px 0 17px;
  border: 1px solid rgba(213, 193, 140, 0.25);
  border-radius: 999px;
  background: rgba(6, 26, 26, 0.84);
  box-shadow: 0 10px 26px rgba(0, 0, 0, 0.24);
  transform: translateX(-50%);
  backdrop-filter: blur(10px);
}

.page-indicator {
  min-width: 142px;
  color: rgba(248, 246, 238, 0.90);
  font-size: 14px;
  line-height: 1;
  text-align: center;
  white-space: nowrap;
}

.dock-divider {
  width: 1px;
  height: 22px;
  margin: 0 5px 0 10px;
  background: rgba(255, 255, 255, 0.14);
}

.fullscreen-button {
  display: grid;
  place-items: center;
  width: 34px;
  height: 34px;
  padding: 0;
  border: 0;
  border-radius: 50%;
  box-shadow: none;
  background: transparent;
}

.fullscreen-button svg { width: 21px; height: 21px; }
.fullscreen-button .exit-icon { display: none; }
.fullscreen-button.is-fullscreen .enter-icon { display: none; }
.fullscreen-button.is-fullscreen .exit-icon { display: block; }

.loading-state {
  position: absolute;
  left: 50%;
  top: 50%;
  z-index: 20;
  display: flex;
  align-items: center;
  gap: 11px;
  padding: 12px 16px;
  border: 1px solid rgba(213, 193, 140, 0.22);
  border-radius: 999px;
  color: rgba(255, 255, 255, 0.85);
  background: rgba(6, 24, 24, 0.88);
  font-size: 14px;
  transform: translate(-50%, -50%);
  transition: opacity 180ms ease, visibility 180ms ease;
}

.loading-state.is-hidden { opacity: 0; visibility: hidden; }

.loading-mark {
  width: 17px;
  height: 17px;
  border: 2px solid rgba(255, 255, 255, 0.25);
  border-top-color: var(--accent);
  border-radius: 50%;
  animation: spin 700ms linear infinite;
}

@keyframes spin { to { transform: rotate(360deg); } }

@media (max-width: 900px) {
  .nav-button { width: 54px; height: 54px; }
  .nav-button svg { width: 24px; height: 24px; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 1ms !important;
    transition-duration: 1ms !important;
  }
}