:root {
  color-scheme: dark;
  font-family: "Inter", "Segoe UI", system-ui, -apple-system, BlinkMacSystemFont, sans-serif;
  --bg: #050505;
  --panel: rgba(255, 255, 255, 0.08);
  --panel-stroke: rgba(255, 255, 255, 0.12);
  --text: #f5f5f5;
  --muted: rgba(255, 255, 255, 0.7);
  --accent: #f3d17a;
  --flip-duration: 0.9s;
  --book-scale: 1;
  --spread-count: 2;
  --page-width: 816px;
  --page-height: 1056px;
}

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

html, body {
  margin: 0;
  min-height: 100vh;
  background: radial-gradient(circle at top, #111 0%, #050505 70%);
  color: var(--text);
}

body {
  display: flex;
  align-items: stretch;
}

.viewer-shell {
  width: 100%;
  min-height: 100vh;
  padding: 1.25rem;
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

.toolbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
  border: 1px solid var(--panel-stroke);
  border-radius: 999px;
  padding: 0.6rem 1rem;
  background: rgba(0, 0, 0, 0.55);
  backdrop-filter: blur(10px);
}

.nav-controls {
  display: inline-flex;
  align-items: center;
  gap: 0.75rem;
}

.tool-group {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
}

.toolbar button,
.toolbar a {
  appearance: none;
  border: 1px solid transparent;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.08);
  color: var(--text);
  font-size: 0.95rem;
  font-weight: 500;
  padding: 0.4rem 0.95rem;
  text-decoration: none;
  cursor: pointer;
  transition: border-color 0.2s ease, background 0.2s ease;
}

.toolbar button:hover,
.toolbar a:hover {
  border-color: var(--accent);
  background: rgba(255, 255, 255, 0.15);
}

.toolbar button:disabled {
  opacity: 0.4;
  cursor: not-allowed;
}

.page-indicator {
  margin: 0;
  font-size: 0.95rem;
  letter-spacing: 0.05em;
  color: var(--muted);
  font-variant-numeric: tabular-nums;
}

.flipbook-region {
  flex: 1;
  min-height: 0;
  border-radius: 1.5rem;
  border: 1px solid var(--panel-stroke);
  background: rgba(255, 255, 255, 0.03);
  padding: 1rem;
  display: flex;
}

.flipbook-scroll {
  width: 100%;
  height: 100%;
  overflow: hidden;
  border-radius: 1.2rem;
  background: rgba(10, 10, 10, 0.7);
  display: flex;
  justify-content: center;
  align-items: center;
  position: relative;
}

.flipbook {
  position: relative;
  width: 100%;
  height: 100%;
  display: flex;
  justify-content: center;
  align-items: center;
}

.book-surface {
  position: relative;
  width: 100%;
  height: 100%;
  border-radius: 1rem;
  background: linear-gradient(120deg, rgba(255, 255, 255, 0.08), rgba(255, 255, 255, 0.01));
  backdrop-filter: blur(8px);
  border: 1px solid rgba(255, 255, 255, 0.07);
  box-shadow: inset 0 0 0 1px rgba(255, 255, 255, 0.03), 0 45px 70px rgba(0, 0, 0, 0.6);
  overflow: hidden;
}

.page-stage {
  position: absolute;
  top: 50%;
  left: 50%;
  width: calc(var(--page-width) * var(--spread-count));
  height: var(--page-height);
  transform: translate(-50%, -50%) scale(var(--book-scale));
  transform-origin: center;
  display: flex;
}

.page-face {
  flex: 1;
  background: #0c0c0c;
  background-size: contain;
  background-repeat: no-repeat;
  background-position: center center;
  border-radius: 0.8rem;
  box-shadow: inset 0 0 0 1px rgba(255, 255, 255, 0.04);
  position: relative;
  overflow: hidden;
}

.page-face.page-left {
  border-radius: 0.8rem 0 0 0.8rem;
}

.page-face.page-right {
  border-radius: 0 0.8rem 0.8rem 0;
}

.page-face.is-empty {
  background: repeating-linear-gradient(
    45deg,
    rgba(255, 255, 255, 0.06),
    rgba(255, 255, 255, 0.06) 12px,
    rgba(255, 255, 255, 0.03) 12px,
    rgba(255, 255, 255, 0.03) 24px
  );
}

.page-link-layer {
  position: absolute;
  inset: 0;
  pointer-events: none;
}

.page-link-hit {
  position: absolute;
  display: block;
  pointer-events: auto;
  text-decoration: none;
  border-radius: 4px;
  background: transparent;
}

.page-link-hit:focus-visible {
  outline: 2px solid rgba(243, 209, 122, 0.9);
  outline-offset: 1px;
}

.flip-overlay {
  position: absolute;
  top: 0;
  left: 0;
  width: var(--page-width);
  height: var(--page-height);
  pointer-events: none;
  opacity: 0;
  transform-style: preserve-3d;
  perspective: 2000px;
}

.flip-overlay .face {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  backface-visibility: hidden;
  background-size: contain;
  background-repeat: no-repeat;
  background-position: center;
  border-radius: 0.75rem;
  box-shadow: 0 25px 35px rgba(0, 0, 0, 0.35);
}

.flip-overlay .face.back {
  transform: rotateY(180deg);
}

.flip-overlay.forward {
  left: var(--page-width);
  transform-origin: left center;
}

.flip-overlay.forward .face {
  border-radius: 0 0.75rem 0.75rem 0;
}

.flip-overlay.backward {
  left: 0;
  transform-origin: right center;
}

.flip-overlay.backward .face {
  border-radius: 0.75rem 0 0 0.75rem;
}

.viewer-shell[data-view-mode="single"] {
  --spread-count: 1;
}

.viewer-shell[data-view-mode="single"] .page-face.page-left {
  display: none;
}

.viewer-shell[data-view-mode="single"] .page-face.page-right {
  border-radius: 0.8rem;
}

.viewer-shell[data-view-mode="single"] .flip-overlay.forward,
.viewer-shell[data-view-mode="single"] .flip-overlay.backward {
  left: 0;
}

.viewer-shell[data-view-mode="single"] .flip-overlay.forward .face,
.viewer-shell[data-view-mode="single"] .flip-overlay.backward .face {
  border-radius: 0.75rem;
}

.flip-overlay.active {
  opacity: 1;
}

.flip-overlay.active.forward {
  animation: flipForward var(--flip-duration) ease forwards;
}

.flip-overlay.active.backward {
  animation: flipBackward var(--flip-duration) ease forwards;
}

@keyframes flipForward {
  0% {
    transform: rotateY(0deg);
    filter: drop-shadow(0 20px 25px rgba(0, 0, 0, 0.5));
  }
  100% {
    transform: rotateY(-180deg);
    filter: drop-shadow(0 10px 15px rgba(0, 0, 0, 0.35));
  }
}

@keyframes flipBackward {
  0% {
    transform: rotateY(0deg);
    filter: drop-shadow(0 20px 25px rgba(0, 0, 0, 0.5));
  }
  100% {
    transform: rotateY(180deg);
    filter: drop-shadow(0 10px 15px rgba(0, 0, 0, 0.35));
  }
}

.loading-state {
  position: absolute;
  inset: 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 0.65rem;
  background: rgba(5, 5, 5, 0.8);
  border-radius: inherit;
  border: 1px dashed rgba(255, 255, 255, 0.2);
}

.loading-state p {
  margin: 0;
  color: var(--muted);
}

.spinner {
  width: 2.5rem;
  height: 2.5rem;
  border-radius: 50%;
  border: 3px solid rgba(255, 255, 255, 0.1);
  border-top-color: var(--accent);
  animation: spin 1s linear infinite;
}

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

.flipbook[data-ready="true"] .loading-state {
  display: none;
}

.noscript-warning {
  margin: 1rem 0 0;
  padding: 1rem;
  background: rgba(255, 255, 255, 0.08);
  border-radius: 0.75rem;
}

@media (max-width: 900px) {
  .viewer-shell {
    padding: 0.75rem;
  }

  .toolbar {
    flex-direction: column;
    border-radius: 1rem;
  }
}

@media (max-width: 600px) {
  .tool-group {
    flex-wrap: wrap;
    justify-content: center;
  }
}