html,
body {
  margin: 0;
  height: 100%;
  background: #f2f2f2;
  overflow: hidden;
  font-family: system-ui, -apple-system, "Hiragino Kaku Gothic ProN", "Noto Sans JP", sans-serif;
}

#book {
  width: 100%;
  height: 100dvh;
  display: flex;
  align-items: center;
  justify-content: center;
  overflow: hidden;
  position: relative;
  background: #f2f2f2;
}

/* ===== ナビゲーション矢印 ===== */
.nav {
  position: fixed;
  inset: 0;
  pointer-events: none;
  z-index: 1000;
}

.nav button {
  pointer-events: auto;
  position: absolute;
  top: 50%;
  transform: translateY(-50%);
  width: 48px;
  height: 48px;
  border-radius: 999px;
  border: 1px solid rgba(0, 0, 0, 0.15);
  background: rgba(255, 255, 255, 0.9);
  font-size: 22px;
  cursor: pointer;
  user-select: none;
  -webkit-tap-highlight-color: transparent;
}

.nav .prev {
  left: 10px;
}

.nav .next {
  right: 10px;
}

.nav button:disabled {
  opacity: 0.45;
  cursor: default;
}

/* ===== 右綴じビューア本体 ===== */
.book-stage {
  position: relative;
  width: min(1100px, 96vw);   /* 少し広げて左右余白を減らす */
  height: min(88vh, 900px);   /* 少し高くして上下余白も減らす */
  perspective: 2000px;
  display: flex;
  align-items: stretch;
  justify-content: center;
}

.book-sheet {
  position: absolute;
  inset: 0;
  display: flex;
  pointer-events: none;
}

.book-single {
  position: absolute;
  inset: 0;
  display: flex;
  justify-content: flex-start;
  align-items: stretch;
  pointer-events: none;
}

.book-page {
  width: 50%;
  height: 100%;
  background: #f2f2f2;
  overflow: hidden;
  position: relative;
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
  transform-style: preserve-3d;
  -webkit-transform-style: preserve-3d;
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.1);
}

.book-page img {
  width: 100%;
  height: 100%;
  object-fit: contain; /* 上下を切らず全体を表示 */
  display: block;
  background: #f2f2f2;
  backface-visibility: hidden;
  -webkit-backface-visibility: hidden;
}

.book-page.left {
  transform-origin: right center;
}

.book-page.right {
  transform-origin: left center;
}

.book-empty {
  width: 50%;
  height: 100%;
  background: transparent;
}

/* ===== ページめくり風アニメーション ===== */
.book-sheet.is-enter-next .book-page.right {
  animation: pageEnterNext 0.55s ease forwards;
}

.book-sheet.is-enter-prev .book-page.left {
  animation: pageEnterPrev 0.55s ease forwards;
}

.book-single.is-enter-next .book-page.left {
  animation: singleToSpread 0.55s ease forwards;
}

@keyframes pageEnterNext {
  0% {
    transform: rotateY(-90deg);
    opacity: 1;
  }
  100% {
    transform: rotateY(0deg);
    opacity: 1;
  }
}

@keyframes pageEnterPrev {
  0% {
    transform: rotateY(90deg);
    opacity: 1;
  }
  100% {
    transform: rotateY(0deg);
    opacity: 1;
  }
}

@keyframes singleToSpread {
  0% {
    transform: rotateY(90deg);
    opacity: 1;
  }
  100% {
    transform: rotateY(0deg);
    opacity: 1;
  }
}

/* ===== スマホ ===== */
@media (max-width: 768px) {
  html,
  body {
    height: 100dvh;
  }

  #book {
    height: 100dvh;
  }

  .book-stage {
    width: 100vw;
    height: 100dvh;
  }

  .book-sheet,
  .book-single {
    display: block;
  }

  .book-page,
  .book-single .book-page {
    width: 100%;
    height: 100%;
    box-shadow: none;
  }

  .book-empty {
    display: none;
  }

  .book-sheet.is-enter-next .book-page.right,
  .book-sheet.is-enter-prev .book-page.left,
  .book-single.is-enter-next .book-page.left {
    animation: none;
  }

  .nav button {
    width: 42px;
    height: 42px;
    font-size: 20px;
  }
}