:root{
  --brand:#4f5fee;
  --brand-dark:#3a46c4;
  --brand-light:#eef0ff;
  --accent:#2f8f4e;
  --ink:#1f2430;
  --muted:#6b7280;
  --border:#e6e8f0;
  --surface:#ffffff;
  --bg:#eef1f7;
  --danger:#d1453b;
  --ok:#2f9e5b;
  --book-w:620px;
  --book-h:876px;
}
*{box-sizing:border-box;}
html,body{
  margin:0;padding:0;height:100%;
  font-family:-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,Helvetica,Arial,sans-serif;
  background:var(--bg);
  color:var(--ink);
  overflow:hidden;
  -webkit-font-smoothing:antialiased;
}
#app{
  display:flex;
  flex-direction:column;
  height:100vh;
  height:100dvh;
}

/* ---------- Topbar (light, modern) ---------- */
.topbar{
  flex:0 0 auto;
  display:flex;
  align-items:center;
  gap:12px;
  padding:12px 18px;
  background:var(--surface);
  color:var(--ink);
  border-bottom:1px solid var(--border);
  z-index:50;
}
.topbar h1{
  font-size:14.5px;
  margin:0;
  font-weight:700;
  flex:1;
  line-height:1.35;
  white-space:nowrap;
  overflow:hidden;
  text-overflow:ellipsis;
  letter-spacing:-.1px;
}
.topbar h1 small{
  display:block;
  font-weight:500;
  font-size:11px;
  color:var(--muted);
}
.icon-btn{
  background:transparent;
  border:1px solid var(--border);
  color:var(--ink);
  border-radius:10px;
  width:38px;height:38px;
  display:flex;align-items:center;justify-content:center;
  cursor:pointer;
  flex:0 0 auto;
  transition:background .15s, border-color .15s;
}
.icon-btn:hover{background:var(--brand-light);border-color:#d8ddfa;}
.icon-btn:active{transform:scale(.94);}

.progress-track{
  height:3px;
  background:var(--border);
  flex:0 0 auto;
}
.progress-fill{
  height:100%;
  width:0%;
  background:linear-gradient(90deg,var(--brand),#8a7bf5);
  transition:width .4s ease;
}

/* ---------- Layout body ---------- */
.body-row{
  flex:1 1 auto;
  display:flex;
  min-height:0;
  position:relative;
}

/* ---------- TOC sidebar ---------- */
.toc{
  width:290px;
  max-width:85vw;
  flex:0 0 auto;
  background:var(--surface);
  border-right:1px solid var(--border);
  overflow-y:auto;
  transform:translateX(-100%);
  transition:transform .25s ease;
  position:absolute;
  top:0;bottom:0;left:0;
  z-index:40;
  box-shadow:8px 0 24px rgba(30,40,80,.08);
}
.toc.open{transform:translateX(0);}
@media (min-width:900px){
  .toc{position:relative;transform:none;box-shadow:none;}
  .toc.open{transform:none;}
}
.toc-header{
  padding:16px 18px;
  font-weight:700;
  color:var(--ink);
  border-bottom:1px solid var(--border);
  font-size:13.5px;
  text-transform:uppercase;
  letter-spacing:.06em;
  color:var(--muted);
}
.toc ul{list-style:none;margin:0;padding:10px;}
.toc li{margin-bottom:2px;}
.toc button{
  width:100%;
  text-align:left;
  background:none;
  border:none;
  border-left:3px solid transparent;
  padding:10px 11px;
  border-radius:9px;
  cursor:pointer;
  font-size:13px;
  color:#333c4d;
  display:flex;
  justify-content:space-between;
  gap:8px;
  transition:background .12s;
}
.toc button:hover{background:#f5f6fc;}
.toc button.active{
  background:var(--brand-light);
  color:var(--brand-dark);
  font-weight:700;
  border-left-color:var(--brand);
}
.toc button .num{opacity:.5;font-size:11px;font-weight:400;}
.toc button.quiz-link::before{
  content:"★ ";
  color:#e0a800;
}
.toc button.active.quiz-link::before{color:#c99400;}

/* ---------- Stage ---------- */
.stage{
  flex:1 1 auto;
  display:flex;
  flex-direction:column;
  align-items:center;
  justify-content:center;
  position:relative;
  min-width:0;
  padding:10px;
  overflow:hidden;
  background:
    radial-gradient(circle at 25% 15%, rgba(79,95,238,.07), transparent 55%),
    radial-gradient(circle at 80% 85%, rgba(47,158,91,.06), transparent 50%),
    var(--bg);
}

/* Floating zoom toolbar */
.zoom-toolbar{
  position:absolute;
  top:14px; right:14px;
  display:flex;
  align-items:center;
  gap:2px;
  background:var(--surface);
  border:1px solid var(--border);
  border-radius:999px;
  padding:5px;
  box-shadow:0 6px 20px rgba(30,40,80,.12);
  z-index:30;
}
.zoom-toolbar button{
  width:30px;height:30px;
  border-radius:50%;
  border:none;
  background:transparent;
  color:var(--ink);
  font-size:16px;
  font-weight:600;
  cursor:pointer;
  display:flex;align-items:center;justify-content:center;
  transition:background .12s;
}
.zoom-toolbar button:hover{background:var(--brand-light);color:var(--brand-dark);}
.zoom-toolbar button:disabled{opacity:.35;cursor:default;background:none;}
.zoom-toolbar .zoom-level{
  font-size:11px;
  color:var(--muted);
  min-width:38px;
  text-align:center;
  font-variant-numeric:tabular-nums;
  font-weight:600;
}
.zoom-toolbar .zoom-sep{
  width:1px;height:18px;background:var(--border);margin:0 2px;
}

.book-wrap{
  perspective:2600px;
  display:flex;
  align-items:center;
  justify-content:center;
  flex:1 1 auto;
  width:100%;
  min-height:0;
  overflow:hidden;
  touch-action:none;
  position:relative;
}
.book-wrap.zoomed{cursor:grab;}
.book-wrap.dragging{cursor:grabbing;}
.book-zoom{
  transform-origin:center center;
  will-change:transform;
}
.book{
  position:relative;
  width:var(--book-w);
  height:var(--book-h);
  transform-style:preserve-3d;
  will-change:transform;
}
.page{
  position:absolute;
  inset:0;
  transform-origin:left center;
  transform-style:preserve-3d;
  transition:transform .7s cubic-bezier(.45,.05,.2,1);
}
.page.no-anim{transition:none !important;}
.face{
  position:absolute;
  inset:0;
  backface-visibility:hidden;
  border-radius:6px;
  overflow:hidden;
  box-shadow:0 2px 14px rgba(30,40,80,.10);
}
.face.front{
  background:#fff;
}
.face.front img{
  width:100%;height:100%;
  display:block;
  object-fit:cover;
}
.face.back{
  transform:rotateY(180deg);
  background:
    repeating-linear-gradient(180deg,#f6f3ec 0px,#f6f3ec 27px,#efece3 28px),
    #f6f3ec;
}
.page-shadow{
  position:absolute;inset:0;
  pointer-events:none !important;
  background:linear-gradient(90deg,rgba(0,0,0,.30),rgba(0,0,0,0) 35%);
  opacity:0;
  transition:opacity .35s ease;
  z-index:6;
}
.page.flipping .page-shadow{opacity:1;}

.click-zone{
  position:absolute;top:0;bottom:0;width:14%;
  cursor:pointer;
  z-index:5;
}
.click-zone.left{left:0;}
.click-zone.right{right:0;}

/* soft ambient shadow under book */
.book::after{
  content:"";
  position:absolute;
  left:5%;right:5%;bottom:-20px;
  height:34px;
  background:radial-gradient(ellipse at center,rgba(40,50,90,.22),transparent 70%);
  filter:blur(6px);
  z-index:-1;
}

/* ---------- Controls (floating dock) ---------- */
.controls{
  flex:0 0 auto;
  display:flex;
  align-items:center;
  justify-content:center;
  gap:12px;
  padding:10px 16px;
  margin:0 auto 14px;
  flex-wrap:wrap;
  background:var(--surface);
  border:1px solid var(--border);
  border-radius:999px;
  box-shadow:0 10px 30px rgba(30,40,80,.12);
  max-width:calc(100% - 20px);
}
.nav-btn{
  background:var(--brand-light);
  color:var(--brand-dark);
  border:none;
  padding:9px 16px;
  border-radius:24px;
  font-size:13px;
  cursor:pointer;
  font-weight:700;
}
.nav-btn:hover:not(:disabled){background:#e1e4ff;}
.nav-btn:disabled{opacity:.35;cursor:default;}
.nav-btn:active:not(:disabled){transform:scale(.96);}
#nextBtn{background:var(--brand);color:#fff;}
#nextBtn:hover:not(:disabled){background:var(--brand-dark);}
#pageIndicator{
  font-size:13px;
  font-variant-numeric:tabular-nums;
  min-width:88px;
  text-align:center;
  color:var(--ink);
  font-weight:700;
}
#pageSlider{
  width:min(220px,32vw);
  accent-color:var(--brand);
}

/* ---------- Cover overlay ---------- */
.cover-overlay{
  position:fixed;inset:0;
  background:linear-gradient(160deg,#3a46c4,#4f5fee 55%,#2f9e5b);
  color:#fff;
  z-index:100;
  display:flex;
  flex-direction:column;
  align-items:center;
  justify-content:center;
  text-align:center;
  padding:24px;
  transition:opacity .5s ease, visibility .5s;
}
.cover-overlay.hidden{opacity:0;visibility:hidden;pointer-events:none;}
.cover-overlay h2{font-size:clamp(20px,4vw,30px);max-width:640px;margin:0 0 8px;}
.cover-overlay p{max-width:560px;opacity:.92;font-size:14px;line-height:1.6;}
.cover-overlay button{
  margin-top:22px;
  background:#fff;
  color:var(--brand-dark);
  border:none;
  padding:13px 30px;
  border-radius:30px;
  font-size:15px;
  font-weight:700;
  cursor:pointer;
  box-shadow:0 6px 18px rgba(0,0,0,.25);
}
.cover-overlay button:hover{transform:translateY(-1px);}

/* ---------- Interactive quiz page styling ----------
   Font-size scales with the book's real rendered width via --book-scale
   (set by JS on <html>), with a hard floor so text/tap-targets never get
   too small on phones. Everything below is in em so it scales together
   with this one root value -- no CSS transform is used, so text always
   renders pixel-sharp at whatever size it ends up being drawn. */
.quiz-page{
  width:100%;height:100%;
  background:#fff;
  padding:2em 1.85em 1.55em;
  overflow-y:auto;
  -webkit-overflow-scrolling:touch;
  font-size:max(12px, calc(13px * var(--book-scale, 1)));
  line-height:1.55;
  display:flex;
  flex-direction:column;
}
.quiz-page .hdr-line{
  text-align:right;
  font-style:italic;
  font-size:.73em;
  color:var(--muted);
  border-bottom:1px solid var(--border);
  padding-bottom:.5em;
  margin-bottom:1.1em;
}
.quiz-page h3{
  font-size:1.15em;
  margin:0 0 .77em;
  color:var(--ink);
  border-bottom:2px solid var(--ink);
  padding-bottom:.4em;
  line-height:1.3;
}
.quiz-page h4{font-size:.96em;margin:1.1em 0 .5em;color:var(--brand-dark);}
.quiz-page .footer-page{
  margin-top:auto;
  text-align:center;
  font-size:.77em;
  color:var(--muted);
  padding-top:.8em;
}
.q-block{
  margin-bottom:.92em;
  padding:.7em .77em;
  border:1px solid var(--border);
  border-radius:.7em;
  background:#fafbfe;
}
.q-block.correct{border-color:var(--ok);background:#eef8f0;}
.q-block.wrong{border-color:var(--danger);background:#fdecea;}
.q-block p.qtext{margin:0 0 .46em;font-weight:600;}
.q-opts label{
  display:block;
  padding:.5em .6em;
  border-radius:.5em;
  cursor:pointer;
  font-size:.93em;
  min-height:1.6em;
}
.q-opts label:hover{background:var(--brand-light);}
.q-opts input{margin-right:.5em;width:1.05em;height:1.05em;vertical-align:middle;accent-color:var(--brand);}
.mark{font-weight:700;margin-left:.46em;font-size:.85em;}
.mark.ok{color:var(--ok);}
.mark.no{color:var(--danger);}

.match-row{
  display:flex;align-items:center;gap:.77em;
  margin-bottom:.7em;
  flex-wrap:wrap;
}
.match-row .term{
  font-weight:700;
  width:7.6em;
  flex:0 0 auto;
}
.match-row select{
  flex:1 1 12em;
  padding:.55em .6em;
  border-radius:.6em;
  border:1px solid var(--border);
  background:#fafbfe;
  font-size:.93em;
  min-height:2.4em;
}
.def-list{
  background:#f6f7fc;
  border:1px solid var(--border);
  border-radius:.7em;
  padding:.77em .92em;
  margin-bottom:1.1em;
  font-size:.93em;
}
.def-list div{margin-bottom:.33em;}

.btn-row{display:flex;gap:.77em;flex-wrap:wrap;margin:.8em 0;}
.btn-mini{
  background:var(--brand);
  color:#fff;
  border:none;
  padding:.62em 1.25em;
  border-radius:1.6em;
  font-size:.93em;
  cursor:pointer;
  font-weight:700;
  min-height:2.6em;
}
.btn-mini:hover{background:var(--brand-dark);}
.btn-mini.secondary{background:#eef0f6;color:var(--ink);}
.btn-mini.secondary:hover{background:#e3e6f0;}
.btn-mini.reset{background:#f1f2f7;color:var(--muted);}
.btn-mini.reset:hover{background:#e6e8f0;}
.score-box{
  margin-top:.46em;
  font-weight:700;
  font-size:1.04em;
  padding:.7em .92em;
  border-radius:.7em;
  background:var(--brand-light);
  color:var(--brand-dark);
  display:none;
}
.score-box.show{display:block;}

.reveal-box{
  border:1px dashed #d8c67a;
  border-radius:.7em;
  padding:.77em .92em;
  background:#fffbe8;
  margin-top:.6em;
}
.reveal-box .content{display:none;margin-top:.46em;font-weight:700;color:#8a6d00;}
.reveal-box.open .content{display:block;}

textarea.reflect{
  width:100%;
  min-height:5.4em;
  border:1px solid var(--border);
  border-radius:.7em;
  padding:.6em;
  font-family:inherit;
  font-size:.93em;
  resize:vertical;
}
.yn-row{
  display:flex;
  align-items:center;
  justify-content:space-between;
  gap:.6em;
  padding:.5em 0;
  border-bottom:1px solid var(--border);
  font-size:.93em;
}
.yn-row .yn-btns{display:flex;gap:.46em;flex:0 0 auto;}
.yn-row button{
  border:1px solid var(--border);
  background:#fff;
  border-radius:1.3em;
  padding:.4em 1em;
  font-size:.85em;
  cursor:pointer;
  min-height:2.2em;
}
.yn-row button.selected{background:var(--brand);color:#fff;border-color:var(--brand);}
.note{
  font-size:.81em;
  color:var(--muted);
  font-style:italic;
  margin-top:.3em;
}

@media (max-width:480px){
  .yn-row{flex-direction:column;align-items:flex-start;gap:.4em;}
  .yn-row .yn-btns{align-self:flex-end;}
  .match-row .term{width:100%;}
}

@media (max-width:640px){
  .topbar h1{font-size:12.5px;}
  .topbar h1 small{font-size:9.5px;}
  .zoom-toolbar{top:10px;right:10px;padding:4px;}
  .zoom-toolbar button{width:26px;height:26px;font-size:14px;}
  .zoom-toolbar .zoom-level{min-width:32px;font-size:10px;}
  .controls{gap:8px;padding:8px 12px;}
}