html, body { height: 100%; overflow: hidden; }

.book-bg {
  position: fixed;
  inset: 0;
  top: 3.4rem;
  background: #0e0c0a;
  display: flex;
  align-items: center;
  justify-content: center;
}

.book-stage {
  position: relative;
  width:  min(90vw, calc((100vh - 3.4rem - 3.5rem) * 1.27));
  height: min(calc(90vw / 1.27), calc(100vh - 3.4rem - 3.5rem));
  perspective: 3500px;
}

.page {
  position: absolute;
  inset: 0;
  transform-origin: left center;
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
  transition: transform 0.82s cubic-bezier(0.645, 0.045, 0.355, 1.000);
  border-radius: 2px;
  overflow: hidden;
  box-shadow: 0 24px 64px rgba(0,0,0,0.85);
}

.page img {
  width: 100%;
  height: 100%;
  object-fit: contain;
  display: block;
  background: #0e0c0a;
}

.page.flipped { transform: rotateY(-180deg); }

.page::after {
  content: '';
  position: absolute;
  inset: 0;
  background: linear-gradient(to left, rgba(0,0,0,0.55) 0%, transparent 60%);
  pointer-events: none;
  opacity: 0;
  transition: opacity 0.41s ease;
}
.page.is-flipping::after { opacity: 1; }

.flip-btn {
  position: fixed;
  top: 50%;
  transform: translateY(-50%);
  width: 40px; height: 40px;
  border-radius: 50%;
  border: 1px solid rgba(255,255,255,0.14);
  background: rgba(255,255,255,0.06);
  color: rgba(255,255,255,0.75);
  font-size: 1rem;
  cursor: pointer;
  display: flex; align-items: center; justify-content: center;
  transition: background 0.2s, opacity 0.2s;
  z-index: 300;
}
.flip-btn:hover { background: rgba(255,255,255,0.16); }
.flip-btn.off   { opacity: 0.18; pointer-events: none; }
#btn-l { left: 1rem; }
#btn-r { right: 1rem; }

.dots {
  position: fixed;
  bottom: 1.1rem;
  left: 50%;
  transform: translateX(-50%);
  display: flex; gap: 9px;
  z-index: 300;
}
.dots span {
  display: block;
  width: 7px; height: 7px;
  border-radius: 50%;
  background: rgba(255,255,255,0.22);
  transition: background 0.3s;
}
.dots span.on { background: rgba(255,255,255,0.82); }

.back-link {
  position: fixed;
  top: calc(3.4rem + 0.7rem);
  left: 1.2rem;
  font-size: 0.7rem;
  font-family: 'Courier New', monospace;
  color: rgba(255,255,255,0.38);
  text-decoration: none;
  z-index: 300;
  transition: color 0.2s;
}
.back-link:hover { color: rgba(255,255,255,0.85); }

.pg-counter {
  position: fixed;
  top: calc(3.4rem + 0.7rem);
  right: 1.2rem;
  font-size: 0.7rem;
  font-family: 'Courier New', monospace;
  color: rgba(255,255,255,0.28);
  z-index: 300;
}

@media (max-width: 600px) {
  .flip-btn { width: 34px; height: 34px; font-size: 0.85rem; }
  #btn-l { left: 0.4rem; }
  #btn-r { right: 0.4rem; }
}