:root {
  --bg: #202124;
  --panel: rgba(20, 21, 24, 0.56);
  --ink: #f7f4ef;
  --muted: #c9c8c4;
  --line: rgba(255,255,255,0.12);
  --page: #fbfaf6;
  --page-shadow: 0 18px 50px rgba(0,0,0,0.34), 0 10px 26px rgba(0,0,0,0.2);
  --flip-speed: 850ms;
  --cover-speed: 980ms;
}

* { box-sizing: border-box; }

html, body {
  height: 100%;
  margin: 0;
}

body {
  background:
    radial-gradient(circle at 50% -10%, rgba(255,255,255,0.06), transparent 36rem),
    linear-gradient(180deg, #2a2b2f 0%, var(--bg) 50%, #18191c 100%);
  color: var(--ink);
  font-family: Helvetica, Arial, sans-serif;
  overflow: hidden;
}

button { font: inherit; }

.app-shell {
  min-height: 100%;
  display: grid;
  grid-template-rows: auto minmax(0, 1fr);
  gap: 12px;
  padding: 18px clamp(16px, 3vw, 32px) 14px;
}

.topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
}

.topbar {
  padding: 14px 16px;
  border-radius: 0;
  background: transparent;
  backdrop-filter: none;
  border: 0;
  box-shadow: none;
}

.identity { min-width: 220px; }

.eyebrow {
  color: var(--muted);
  font-size: 12px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

h1 {
  margin: 2px 0 0;
  font-size: clamp(26px, 4vw, 42px);
  line-height: 0.94;
  font-weight: 700;
  letter-spacing: -0.045em;
  text-transform: uppercase;
}

.controls {
  display: flex;
  align-items: center;
  gap: 10px;
  flex-wrap: wrap;
  justify-content: flex-end;
}

.control-btn,
.text-btn,
.mini-btn {
  border: 1px solid var(--line);
  background: rgba(255,255,255,0.08);
  color: var(--ink);
  cursor: pointer;
  transition: transform 160ms ease, background 160ms ease, border-color 160ms ease, opacity 160ms ease;
}

.control-btn:hover,
.text-btn:hover,
.mini-btn:hover {
  background: rgba(255,255,255,0.16);
  border-color: rgba(255,255,255,0.28);
}

.control-btn:active,
.text-btn:active,
.mini-btn:active { transform: translateY(1px); }

.control-btn:disabled,
.text-btn:disabled,
.mini-btn:disabled {
  opacity: 0.35;
  cursor: not-allowed;
}

.control-btn {
  width: 42px;
  height: 42px;
  border-radius: 999px;
  font-size: 32px;
  line-height: 36px;
  display: grid;
  place-items: center;
  padding-bottom: 3px;
}

.text-btn {
  min-height: 38px;
  padding: 0 14px;
  border-radius: 999px;
  font-size: 13px;
  letter-spacing: 0.02em;
}

.page-count {
  color: var(--muted);
  min-width: 132px;
  text-align: center;
  font-size: 14px;
  font-variant-numeric: tabular-nums;
}

.zoom-controls {
  display: flex;
  align-items: center;
  gap: 8px;
  min-height: 38px;
  padding: 0 10px;
  border-radius: 999px;
  border: 1px solid var(--line);
  background: rgba(0,0,0,0.14);
}

.mini-btn {
  width: 28px;
  height: 28px;
  border-radius: 999px;
  display: grid;
  place-items: center;
  padding: 0;
  font-size: 18px;
  line-height: 1;
}

#zoomRange {
  width: clamp(92px, 11vw, 150px);
  accent-color: #f7f4ef;
}

.zoom-readout {
  min-width: 42px;
  color: var(--muted);
  font-size: 12px;
  text-align: right;
  font-variant-numeric: tabular-nums;
}

.stage {
  display: grid;
  place-items: center;
  min-height: 0;
  perspective: 3000px;
  overflow: hidden;
  user-select: none;
  touch-action: pan-y;
}

.stage.dragging {
  cursor: grabbing;
}

.viewport {
  position: relative;
  display: grid;
  place-items: center;
  width: 100%;
  height: 100%;
  transform-origin: center center;
  transform: translate3d(0,0,0) scale(1);
  transition: transform 180ms ease;
  will-change: transform;
}

.stage.dragging .viewport,
.stage.is-zoomed .viewport {
  transition: none;
}

.closed-book {
  position: absolute;
  width: min(64vw, calc((100vh - 205px) * 1.5454545));
  aspect-ratio: 17 / 11;
  display: block;
  transform-style: preserve-3d;
  filter: drop-shadow(0 28px 46px rgba(0,0,0,0.34));
  z-index: 4;
}

.cover-board {
  position: absolute;
  inset: 0;
  overflow: hidden;
  border-radius: 14px 18px 18px 14px;
  background: #fff;
  box-shadow: var(--page-shadow), inset -18px 0 28px rgba(0,0,0,0.10);
  transform-style: preserve-3d;
}

.cover-board::before {
  content: "";
  position: absolute;
  inset: 0;
  z-index: 3;
  pointer-events: none;
  box-shadow: inset 0 0 0 1px rgba(0,0,0,0.12), inset 11px 0 0 rgba(0,0,0,0.06);
}

.cover-board img,
.sheet img,
.turn-page img {
  width: 100%;
  height: 100%;
  display: block;
  object-fit: contain;
  object-position: center;
  background: #fff;
  pointer-events: none;
  -webkit-user-drag: none;
}

.cover-gloss {
  position: absolute;
  inset: 0;
  z-index: 2;
  pointer-events: none;
  background: linear-gradient(110deg, rgba(255,255,255,0.05) 20%, rgba(255,255,255,0.42) 48%, rgba(0,0,0,0.12) 70%);
  mix-blend-mode: soft-light;
  opacity: 0.75;
}

.open-book {
  position: absolute;
  width: min(96vw, calc((100vh - 205px) * 3.0909091));
  aspect-ratio: 34 / 11;
  transform-style: preserve-3d;
  filter: drop-shadow(0 24px 46px rgba(0,0,0,0.30));
  opacity: 0;
  pointer-events: none;
  z-index: 2;
}

.mode-open .open-book {
  opacity: 1;
  pointer-events: auto;
}

.mode-open .closed-book {
  opacity: 0;
  pointer-events: none;
}

.mode-cover .open-book {
  opacity: 0;
  pointer-events: none;
}

.mode-cover .closed-book {
  opacity: 1;
  pointer-events: auto;
}

.stage.opening .closed-book {
  animation: coverOpen var(--cover-speed) cubic-bezier(.52,.03,.19,1) forwards;
}

.stage.opening .open-book {
  opacity: 1;
  animation: bookReveal var(--cover-speed) ease forwards;
}

.stage.closing .closed-book {
  animation: coverClose var(--cover-speed) cubic-bezier(.52,.03,.19,1) forwards;
}

.stage.closing .open-book {
  opacity: 1;
  animation: bookHide var(--cover-speed) ease forwards;
}

.spread {
  position: absolute;
  inset: 0;
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0;
}

.spread-under {
  opacity: 0;
  z-index: 1;
}

.spread-under.active { opacity: 1; }

.spread-current { z-index: 2; }

.sheet {
  position: relative;
  overflow: hidden;
  background: var(--page);
  box-shadow: var(--page-shadow);
}

.left-sheet { border-radius: 12px 0 0 12px; }
.right-sheet { border-radius: 0 12px 12px 0; }

.sheet.blank {
  background:
    linear-gradient(90deg, rgba(0,0,0,0.03), transparent 25%),
    #f8f4eb;
}

.sheet.blank img { display: none; }

.sheet::before,
.turn-page::before {
  content: "";
  position: absolute;
  inset: 0;
  box-shadow: inset 0 0 0 1px rgba(0,0,0,0.08);
  pointer-events: none;
  z-index: 4;
}

.sheet::after {
  content: "";
  position: absolute;
  inset: 0;
  z-index: 3;
  pointer-events: none;
  opacity: 0;
  transition: opacity 180ms ease;
  background: radial-gradient(circle at var(--mx, 50%) var(--my, 50%), rgba(255,255,255,0.34), transparent 12rem);
}

.open-book:hover .sheet::after,
.closed-book:hover .cover-board::after { opacity: 1; }

.cover-board::after {
  content: "";
  position: absolute;
  inset: 0;
  z-index: 2;
  pointer-events: none;
  opacity: 0;
  transition: opacity 180ms ease;
  background: radial-gradient(circle at var(--mx, 50%) var(--my, 50%), rgba(255,255,255,0.34), transparent 13rem);
}

.current-hide-right .right-sheet,
.current-hide-left .left-sheet { opacity: 0; }

.turn-page {
  position: absolute;
  top: 0;
  bottom: 0;
  width: 50%;
  background: var(--page);
  box-shadow: var(--page-shadow);
  display: none;
  overflow: hidden;
  backface-visibility: hidden;
  transform-style: preserve-3d;
  z-index: 3;
}

.turn-page.active { display: block; }

.turn-next {
  right: 0;
  border-radius: 0 12px 12px 0;
  transform-origin: left center;
}

.turn-prev {
  left: 0;
  border-radius: 12px 0 0 12px;
  transform-origin: right center;
}

.turn-next.active { animation: flipNextSpread var(--flip-speed) cubic-bezier(.58,.02,.22,1) forwards; }
.turn-prev.active { animation: flipPrevSpread var(--flip-speed) cubic-bezier(.58,.02,.22,1) forwards; }

.page-sheen {
  position: absolute;
  inset: 0;
  z-index: 5;
  pointer-events: none;
  opacity: 0;
  background: linear-gradient(90deg, rgba(255,255,255,0.04), rgba(255,255,255,0.35), rgba(0,0,0,0.18));
}

.turn-next.active .page-sheen,
.turn-prev.active .page-sheen { animation: sheen var(--flip-speed) ease-in-out forwards; }

.spine {
  position: absolute;
  top: 0;
  bottom: 0;
  left: calc(50% - 13px);
  width: 26px;
  z-index: 6;
  pointer-events: none;
  background:
    linear-gradient(90deg,
      rgba(0,0,0,0.18) 0%,
      rgba(255,255,255,0.08) 25%,
      rgba(0,0,0,0.28) 48%,
      rgba(255,255,255,0.06) 52%,
      rgba(0,0,0,0.12) 100%);
  opacity: 0.60;
  filter: blur(0.2px);
}


@keyframes coverOpen {
  0% { transform: translateX(0) rotateY(0deg) scale(1); opacity: 1; }
  46% { transform: translateX(-26%) rotateY(-82deg) scale(1.04); opacity: 0.96; }
  100% { transform: translateX(-42%) rotateY(-165deg) scale(1.03); opacity: 0; }
}

@keyframes coverClose {
  0% { transform: translateX(-42%) rotateY(-165deg) scale(1.03); opacity: 0; }
  45% { transform: translateX(-24%) rotateY(-78deg) scale(1.04); opacity: 0.98; }
  100% { transform: translateX(0) rotateY(0deg) scale(1); opacity: 1; }
}

@keyframes bookReveal {
  0%, 28% { transform: scale(0.82); opacity: 0; }
  100% { transform: scale(1); opacity: 1; }
}

@keyframes bookHide {
  0% { transform: scale(1); opacity: 1; }
  72%, 100% { transform: scale(0.82); opacity: 0; }
}

@keyframes flipNextSpread {
  0% { transform: rotateY(0deg); box-shadow: var(--page-shadow); }
  48% { transform: rotateY(-96deg) translateZ(10px); box-shadow: -48px 18px 70px rgba(0,0,0,0.45); }
  100% { transform: rotateY(-180deg); box-shadow: -10px 10px 26px rgba(0,0,0,0.08); }
}

@keyframes flipPrevSpread {
  0% { transform: rotateY(0deg); box-shadow: var(--page-shadow); }
  48% { transform: rotateY(96deg) translateZ(10px); box-shadow: 48px 18px 70px rgba(0,0,0,0.45); }
  100% { transform: rotateY(180deg); box-shadow: 10px 10px 26px rgba(0,0,0,0.08); }
}

@keyframes sheen {
  0%, 100% { opacity: 0; }
  46%, 62% { opacity: 0.98; }
}

@media (max-width: 1100px) {
  .open-book { width: 98vw; }
  .closed-book { width: 76vw; }
}

@media (max-width: 760px) {
  body { overflow: auto; }

  .app-shell {
    min-height: 100dvh;
    padding: 14px;
    gap: 12px;
  }

  .topbar {
    align-items: flex-start;
    flex-direction: column;
  }

  .controls { justify-content: flex-start; }
  .stage { min-height: 48vh; }
  .open-book { width: 98vw; }
  .closed-book { width: 88vw; }
  .page-count { text-align: left; }
}

@media (prefers-reduced-motion: reduce) {
  :root { --flip-speed: 1ms; --cover-speed: 1ms; }
  .page-sheen, .cover-gloss { display: none; }
}