:root {
  --bg: #17151b;
  --text: #ece5d8;
  --muted: #a69d8f;
  --accent: #c9a96a;
  --page-w: 420px;
  --page-h: 700px;
}
* { box-sizing: border-box; }
html, body { margin: 0; height: 100%; }
body {
  background: radial-gradient(ellipse at 50% 30%, #262129 0%, var(--bg) 70%);
  color: var(--text);
  font-family: "Noto Serif TC", serif;
  display: flex; flex-direction: column; min-height: 100vh;
  overflow-x: hidden;
}
header { text-align: center; padding: 20px 16px 4px; }
header a { color: var(--accent); font-size: 14px; text-decoration: none; }

#stage { position: relative; flex: 1; min-height: 300px; touch-action: pan-y; }
#scaler {
  position: absolute; top: 0; left: 0;
  width: calc(var(--page-w) * 2); height: var(--page-h);
  transform-origin: 0 0;
  transition: left .7s cubic-bezier(.3,.1,.2,1);
}
.book { position: relative; width: 100%; height: 100%; perspective: 2600px; }

.leaf {
  position: absolute; top: 0; left: var(--page-w);
  width: var(--page-w); height: var(--page-h);
  transform-origin: left center;
  transform-style: preserve-3d;
  transition: transform .9s cubic-bezier(.35,.1,.2,1);
}
.leaf.flipped { transform: rotateY(-180deg); }
.face {
  position: absolute; inset: 0; overflow: hidden;
  backface-visibility: hidden; -webkit-backface-visibility: hidden;
}
.face.back { transform: rotateY(180deg); }

/* 內頁紙 */
.paper {
  background-color: #efe5cf;
  background-image:
    linear-gradient(90deg, transparent 54px, rgba(185,80,70,.35) 54px, rgba(185,80,70,.35) 55px, transparent 55px,
                            transparent 58px, rgba(185,80,70,.35) 58px, rgba(185,80,70,.35) 59px, transparent 59px),
    repeating-linear-gradient(180deg, transparent 0 33px, rgba(95,130,165,.22) 33px 34px);
  background-position: 0 0, 0 50px;
}
.face.front.paper { border-radius: 0 4px 4px 0; }
.face.back.paper  { border-radius: 4px 0 0 4px; }
.face.back.paper  { background-image:
    linear-gradient(270deg, transparent 54px, rgba(185,80,70,.35) 54px, rgba(185,80,70,.35) 55px, transparent 55px,
                            transparent 58px, rgba(185,80,70,.35) 58px, rgba(185,80,70,.35) 59px, transparent 59px),
    repeating-linear-gradient(180deg, transparent 0 33px, rgba(95,130,165,.22) 33px 34px); }
/* 書脊陰影與紙張邊緣 */
.face.front::after, .face.back::after { content: ""; position: absolute; inset: 0; pointer-events: none; }
.face.front::after { background:
    linear-gradient(90deg, rgba(60,40,20,.28), rgba(60,40,20,0) 9%),
    radial-gradient(ellipse at 50% 50%, rgba(0,0,0,0) 60%, rgba(110,75,35,.16) 100%); }
.face.back::after  { background:
    linear-gradient(270deg, rgba(60,40,20,.28), rgba(60,40,20,0) 9%),
    radial-gradient(ellipse at 50% 50%, rgba(0,0,0,0) 60%, rgba(110,75,35,.16) 100%); }

.slots {
  position: absolute; inset: 18px 28px 30px;
  display: flex; flex-direction: column; justify-content: flex-start; gap: 14px;
}
.slot {
  position: relative; margin: 0; width: 100%; aspect-ratio: 600 / 350;
  cursor: zoom-in; border: 0; padding: 0; background: none;
  filter: drop-shadow(0 2px 3px rgba(60,40,20,.35));
}
.slot img { width: 100%; height: 100%; display: block; }
.tape {
  position: absolute; top: -9px; left: 50%; width: 86px; height: 22px; margin-left: -43px;
  background: rgba(226,214,180,.72);
  box-shadow: 0 1px 1px rgba(0,0,0,.08);
}
.pno { position: absolute; bottom: 8px; font-size: 13px; color: rgba(70,55,40,.6); z-index: 1; }
.front .pno { right: 22px; }
.back .pno { left: 22px; }
.empty-note {
  position: absolute; inset: 0; display: flex; align-items: center; justify-content: center;
  color: rgba(70,55,40,.55); font-family: "LXGW WenKai TC", "Noto Serif TC", serif; font-size: 20px;
}

/* 封面 */
.cover {
  background-color: #3b3a2e;
  background-image:
    repeating-linear-gradient(45deg, rgba(255,255,255,.025) 0 2px, transparent 2px 5px),
    repeating-linear-gradient(-45deg, rgba(0,0,0,.05) 0 2px, transparent 2px 6px),
    radial-gradient(ellipse at 40% 35%, rgba(255,255,255,.06), rgba(0,0,0,.28) 80%);
  border-radius: 0 6px 6px 0;
  box-shadow: inset 6px 0 10px rgba(0,0,0,.35);
}
.cover.backcover { border-radius: 6px 0 0 6px; box-shadow: inset -6px 0 10px rgba(0,0,0,.35); }
.label {
  position: absolute; left: 50%; top: 24%; transform: translateX(-50%);
  width: 260px; padding: 22px 18px 18px; text-align: center;
  background: #ece2c9; color: #3b3326;
  border: 1px solid rgba(90,70,40,.4);
  box-shadow: 0 1px 2px rgba(0,0,0,.35), inset 0 0 0 5px #ece2c9, inset 0 0 0 6px rgba(90,70,40,.45);
}
.label h1 { margin: 0; font-size: 26px; font-weight: 600; letter-spacing: .12em; }
.label p { margin: 8px 0 0; font-size: 14px; color: #6e6250; font-family: "LXGW WenKai TC", "Noto Serif TC", serif; }
.endpaper { background: #d9cdb2; }
.endpaper.back { border-radius: 4px 0 0 4px; }
.endpaper.front { border-radius: 0 4px 4px 0; }
.intro {
  position: absolute; inset: 0; display: flex; align-items: center; justify-content: center;
  padding: 48px; text-align: center; white-space: pre-line;
  font-family: "LXGW WenKai TC", "Noto Serif TC", serif; font-size: 19px; line-height: 2; color: #4a3f31;
}

nav {
  display: flex; align-items: center; justify-content: center; gap: 18px;
  padding: 10px 16px 22px;
}
nav button {
  font: inherit; font-size: 15px; color: var(--text); background: #221f27;
  border: 1px solid #3a3541; border-radius: 6px; padding: 8px 18px; cursor: pointer;
}
nav button:disabled { opacity: .35; cursor: default; }
#pos { color: var(--muted); font-size: 14px; min-width: 7em; text-align: center; }

/* 放大檢視 */
#lightbox {
  position: fixed; inset: 0; background: rgba(10,8,12,.86);
  display: none; align-items: center; justify-content: center; padding: 16px; z-index: 1000;
  cursor: zoom-out;
}
#lightbox.show { display: flex; }
#lightbox img { max-width: min(100%, 1200px); max-height: 90vh; box-shadow: 0 10px 40px rgba(0,0,0,.6); }
.msg { text-align: center; color: var(--muted); padding: 40px 16px; }

@media (prefers-reduced-motion: reduce) {
  .leaf, #scaler { transition: none; }
}