*,*::before,*::after{box-sizing:border-box;margin:0;padding:0}
:root{
  --bg:#f0f4f8;
  --card:#ffffff;
  --primary:#1e40af;
  --primary-light:#3b82f6;
  --primary-dark:#1e3a8a;
  --success:#16a34a;
  --success-bg:#dcfce7;
  --success-light:#bbf7d0;
  --error:#dc2626;
  --error-bg:#fee2e2;
  --error-light:#fecaca;
  --muted:#64748b;
  --muted-light:#94a3b8;
  --border:#e2e8f0;
  --text:#0f172a;
  --text-secondary:#475569;
  --radius:14px;
  --radius-sm:10px;
  --shadow:0 1px 3px rgba(0,0,0,.08),0 4px 12px rgba(0,0,0,.06);
  --shadow-sm:0 1px 2px rgba(0,0,0,.06);
  
}
@media(prefers-color-scheme:dark){
  :root{
    --bg:#0f172a;
    --card:#1e293b;
    --primary:#3b82f6;
    --primary-light:#60a5fa;
    --primary-dark:#2563eb;
    --success:#22c55e;
    --success-bg:#052e16;
    --success-light:#166534;
    --error:#ef4444;
    --error-bg:#450a0a;
    --error-light:#7f1d1d;
    --muted:#94a3b8;
    --muted-light:#64748b;
    --border:#334155;
    --text:#f1f5f9;
    --text-secondary:#94a3b8;
    --shadow:0 1px 3px rgba(0,0,0,.3),0 4px 12px rgba(0,0,0,.2);
    --shadow-sm:0 1px 2px rgba(0,0,0,.2);
  }
}
html{scroll-behavior:smooth;}
body{
  font-family:-apple-system,BlinkMacSystemFont,"SF Pro Text","Segoe UI",Arial,sans-serif;
  background:var(--bg);color:var(--text);min-height:100vh;
  font-size:15px;line-height:1.5;-webkit-text-size-adjust:100%;
}
.app{max-width:680px;margin:0 auto;display:flex;flex-direction:column;min-height:100vh;}

/* ── Top bar ── */
.topbar{
  background:var(--primary);color:#fff;
  padding:12px 16px 10px;
  padding-top:calc(12px + env(safe-area-inset-top));
  position:sticky;top:0;z-index:100;
  box-shadow:0 2px 8px rgba(30,64,175,.3);
}
.topbar-row1{display:flex;align-items:center;justify-content:space-between;gap:8px;}
.app-title{font-size:16px;font-weight:700;letter-spacing:-.01em;}
.ch-badge{
  font-size:12px;font-weight:600;background:rgba(255,255,255,.18);
  padding:4px 10px;border-radius:20px;white-space:nowrap;
  max-width:58%;overflow:hidden;text-overflow:ellipsis;
}
.progress-row{display:flex;align-items:center;gap:8px;margin-top:8px;}
.prog-bar{flex:1;height:6px;background:rgba(255,255,255,.25);border-radius:3px;overflow:hidden;}
.prog-fill{height:100%;background:#fff;border-radius:3px;transition:width .4s ease;}
.prog-label{font-size:12px;font-weight:700;opacity:.9;white-space:nowrap;min-width:36px;text-align:right;}

/* ── Chapter nav ── */
.ch-nav-wrap{
  background:var(--card);border-bottom:1px solid var(--border);
  overflow-x:auto;-webkit-overflow-scrolling:touch;scrollbar-width:none;
  position:sticky;top:calc(var(--topbar-actual, 60px));z-index:99;
}
.ch-nav-wrap::-webkit-scrollbar{display:none;}
.ch-nav{display:flex;gap:0;padding:0 4px;width:max-content;min-width:100%;}
.ch-btn{
  flex-shrink:0;padding:10px 14px;min-height:44px;
  border:none;background:none;cursor:pointer;
  font-size:12px;font-weight:600;color:var(--muted);
  border-bottom:3px solid transparent;
  transition:all .15s;white-space:nowrap;
  touch-action:manipulation;-webkit-tap-highlight-color:transparent;
  position:relative;display:flex;align-items:center;
}
.ch-btn:hover{color:var(--primary);}
.ch-btn.active{color:var(--primary);border-bottom-color:var(--primary);}
.ch-btn.done-good{color:var(--success);}
.ch-btn.done-good.active{border-bottom-color:var(--success);}
.ch-btn.done-bad{color:var(--error);}
.ch-btn.done-bad.active{border-bottom-color:var(--error);}
.ch-dot{position:absolute;top:6px;right:4px;width:6px;height:6px;border-radius:50%;display:none;}
.ch-btn.done-good .ch-dot{background:var(--success);display:block;}
.ch-btn.done-bad .ch-dot{background:var(--error);display:block;}

/* ── Question area ── */
.q-area{flex:1;padding:12px 12px 0;}
.card{
  background:var(--card);border-radius:var(--radius);
  box-shadow:var(--shadow);padding:18px 16px 16px;
  scroll-margin-top:calc(var(--nav-actual, 110px) + 8px);
}
.card.anim-fwd{animation:slideInFwd .22s ease;}
.card.anim-back{animation:slideInBack .22s ease;}
@keyframes slideInFwd{from{opacity:0;transform:translateX(18px);}to{opacity:1;transform:none;}}
@keyframes slideInBack{from{opacity:0;transform:translateX(-18px);}to{opacity:1;transform:none;}}

.card-head{display:flex;align-items:center;justify-content:space-between;margin-bottom:12px;}
.qnum-badge{
  font-size:12px;font-weight:700;color:var(--primary);
  background:#eff6ff;padding:4px 10px;border-radius:20px;
  letter-spacing:.04em;text-transform:uppercase;
}
@media(prefers-color-scheme:dark){.qnum-badge{background:#1e3a8a;color:#93c5fd;}}
.type-badge{
  font-size:12px;font-weight:600;color:var(--muted);
  padding:4px 10px;border-radius:20px;border:1px solid var(--border);
}
.ctx-box{
  background:color-mix(in srgb,var(--primary-light) 10%,var(--card));
  border-left:3px solid var(--primary-light);
  border-radius:0 8px 8px 0;padding:9px 12px;
  font-size:13px;color:var(--text-secondary);margin-bottom:12px;line-height:1.5;
}
.qtext{font-size:16px;font-weight:600;margin-bottom:16px;line-height:1.55;color:var(--text);}
@media(max-width:400px){.qtext{font-size:15px;}}

/* ── Options ── */
.options{display:flex;flex-direction:column;gap:9px;}
.opt-btn{
  display:flex;align-items:center;gap:10px;
  padding:12px 14px;border-radius:var(--radius-sm);
  border:2px solid var(--border);background:var(--card);
  cursor:pointer;text-align:left;font-size:14px;line-height:1.45;
  transition:border-color .12s,background .12s,transform .08s;
  width:100%;min-height:52px;box-shadow:var(--shadow-sm);
  touch-action:manipulation;-webkit-tap-highlight-color:transparent;
  overflow-wrap:break-word;word-break:break-word;
}
@media(hover:hover){.opt-btn:hover:not(:disabled){border-color:var(--primary-light);background:#f5faff;}}
.opt-btn:active:not(:disabled){transform:scale(.986);background:#ebf4ff;}
.opt-letter{
  font-weight:700;min-width:26px;height:26px;width:26px;border-radius:50%;
  background:var(--border);color:var(--text-secondary);
  display:flex;align-items:center;justify-content:center;
  font-size:12px;flex-shrink:0;transition:all .12s;
}
.opt-btn.correct{border-color:var(--success);background:var(--success-bg);}
.opt-btn.correct .opt-letter{background:var(--success);color:#fff;}
.opt-btn.wrong{border-color:var(--error);background:var(--error-bg);}
.opt-btn.wrong .opt-letter{background:var(--error);color:#fff;}
.opt-btn.reveal{border-color:var(--success);background:var(--success-bg);opacity:.75;}
.opt-btn.reveal .opt-letter{background:var(--success);color:#fff;}
.opt-btn:disabled{cursor:default;transform:none;}
.opt-btn.selected{border-color:var(--primary);background:#f0f4ff;}
.opt-btn.selected .opt-letter{background:var(--primary);color:#fff;}
.multi-hint{font-size:13px;color:var(--muted);margin-bottom:10px;font-style:italic;}

/* ── Feedback sheet ── */
.feedback-sheet{
  display:none;margin-top:14px;border-radius:var(--radius-sm);
  padding:12px 14px;font-size:14px;font-weight:600;
  animation:feedIn .2s ease;
}
@keyframes feedIn{from{opacity:0;transform:translateY(6px);}to{opacity:1;transform:none;}}
.feedback-sheet.show{display:flex;align-items:center;gap:10px;}
.feedback-sheet.ok{background:var(--success-bg);color:var(--success);border:1px solid var(--success-light);}
.feedback-sheet.fail{background:var(--error-bg);color:var(--error);border:1px solid var(--error-light);}
.feed-icon{font-size:20px;flex-shrink:0;}
.feed-body{flex:1;display:flex;flex-direction:column;gap:4px;}
.feed-title{font-weight:700;font-size:15px;}
.feed-detail{font-size:13px;font-weight:500;opacity:.85;line-height:1.4;white-space:pre-line;}
@media(max-width:400px){
  .feedback-sheet.show{flex-wrap:wrap;}
}

/* ── Controls (sticky bottom) ── */
.controls{
  position:sticky;bottom:0;background:var(--bg);
  padding:10px 12px;
  padding-bottom:calc(10px + env(safe-area-inset-bottom));
  display:flex;justify-content:space-between;align-items:center;gap:8px;
  border-top:1px solid var(--border);z-index:50;
}
.btn{
  padding:11px 20px;border-radius:var(--radius-sm);border:none;
  font-size:14px;font-weight:700;cursor:pointer;transition:all .12s;
  touch-action:manipulation;-webkit-tap-highlight-color:transparent;
  min-height:48px;letter-spacing:.01em;
}
.btn-primary{background:var(--primary);color:#fff;box-shadow:0 2px 8px rgba(30,64,175,.28);}
@media(hover:hover){.btn-primary:hover{background:var(--primary-dark);}}
.btn-primary:active{transform:scale(.97);}
.btn-outline{background:var(--card);color:var(--text-secondary);border:2px solid var(--border);box-shadow:var(--shadow-sm);}
@media(hover:hover){.btn-outline:hover{border-color:var(--primary-light);color:var(--primary);}}
.btn-outline:active{transform:scale(.97);}
.btn:disabled{opacity:.35;cursor:default;transform:none;}
.btn-eval{background:var(--success);color:#fff;box-shadow:0 2px 8px rgba(22,163,74,.28);}
@media(hover:hover){.btn-eval:hover{background:#15803d;}}
.btn-eval:active{transform:scale(.97);}

.nav-counter{font-size:13px;color:var(--muted);font-weight:600;text-align:center;flex-shrink:0;}
@media(max-width:420px){.btn{padding:11px 12px;font-size:13px;}}

/* ── Matching ── */
.match-wrap{display:flex;flex-direction:column;gap:10px;}
.match-hint{font-size:13px;color:var(--muted);font-style:italic;margin-bottom:2px;}
.match-cols{display:grid;grid-template-columns:1fr 1fr;gap:10px;}
@media(max-width:600px){.match-cols{grid-template-columns:1fr;}}
.match-col-label{font-size:11px;font-weight:700;color:var(--muted-light);text-transform:uppercase;letter-spacing:.08em;margin-bottom:6px;}
.match-items,.match-cats{display:flex;flex-direction:column;gap:6px;}
.match-chip{
  padding:10px 12px;border-radius:var(--radius-sm);border:2px solid var(--border);
  background:var(--card);cursor:pointer;font-size:13px;line-height:1.4;
  transition:all .12s;touch-action:manipulation;-webkit-tap-highlight-color:transparent;
  min-height:48px;display:flex;align-items:center;gap:8px;
  text-align:left;width:100%;box-shadow:var(--shadow-sm);
  overflow-wrap:break-word;word-break:break-word;
}
@media(hover:hover){.match-chip:hover:not(:disabled){border-color:var(--primary-light);background:#f5faff;}}
.match-chip:active:not(:disabled){transform:scale(.986);}
.match-chip.selected-item{border-color:var(--primary);background:#f0f4ff;}
.match-chip.selected-item .chip-num{background:var(--primary);color:#fff;}
.match-chip.paired{border-color:var(--muted-light);background:color-mix(in srgb,var(--muted-light) 8%,var(--card));}
.match-chip.correct{border-color:var(--success);background:var(--success-bg);}
.match-chip.correct .chip-num,.match-chip.correct .chip-letter{background:var(--success);color:#fff;}
.match-chip.wrong{border-color:var(--error);background:var(--error-bg);}
.match-chip.wrong .chip-num,.match-chip.wrong .chip-letter{background:var(--error);color:#fff;}
.match-chip:disabled{cursor:default;transform:none;}
.chip-num,.chip-letter{
  font-weight:700;min-width:24px;height:24px;width:24px;border-radius:50%;
  background:var(--border);color:var(--text-secondary);
  display:flex;align-items:center;justify-content:center;font-size:12px;flex-shrink:0;
}
.match-badge{
  display:inline-flex;align-items:center;gap:3px;
  background:var(--primary);color:#fff;border-radius:12px;
  font-size:12px;font-weight:700;padding:2px 8px;margin-top:3px;
  flex-shrink:0;white-space:nowrap;
}
.match-badge.ok{background:var(--success);}
.match-badge.bad{background:var(--error);}
.cat-has-match{background:#f0fdf4 !important;border-color:var(--success-light) !important;}
.undo-badge{
  margin-left:auto;font-size:12px;color:var(--muted);background:none;border:none;
  cursor:pointer;padding:2px 4px;flex-shrink:0;touch-action:manipulation;
}
.waiting-cat .match-chip[data-letter]{animation:pulse-border .7s ease-in-out infinite alternate;}
@keyframes pulse-border{from{border-color:var(--border);}to{border-color:var(--primary-light);box-shadow:0 0 0 3px rgba(59,130,246,0.3);}}

/* ── Sign matching ── */
.sign-wrap{display:flex;flex-direction:column;gap:10px;}
.sign-pool{
  display:flex;flex-wrap:wrap;gap:6px;
  background:color-mix(in srgb,var(--muted-light) 8%,var(--card));
  border:1px dashed var(--border);border-radius:var(--radius-sm);
  padding:10px;min-height:48px;
}
.sign-pool-label{font-size:11px;font-weight:700;color:var(--muted-light);text-transform:uppercase;letter-spacing:.08em;margin-bottom:4px;}
@media(max-width:480px){
  .sign-pool{flex-direction:column;}
  .term-chip{width:100%;justify-content:center;}
}
.sign-targets{display:flex;flex-direction:column;gap:8px;}
.sign-row{
  display:flex;align-items:center;gap:10px;background:var(--card);
  border:1px solid var(--border);border-radius:var(--radius-sm);
  padding:8px 12px;min-height:56px;box-shadow:var(--shadow-sm);
}
.sign-img{width:44px;height:44px;object-fit:contain;flex-shrink:0;border-radius:4px;}
.sign-lbl{font-size:12px;font-weight:700;color:var(--muted);min-width:24px;flex-shrink:0;}
.sign-slot{
  flex:1;min-height:38px;border:2px dashed var(--border);border-radius:8px;
  padding:4px;display:flex;flex-wrap:wrap;gap:4px;align-items:center;
  transition:all .12s;cursor:pointer;
}
.sign-slot:hover{border-color:var(--primary-light);}
.sign-slot.correct-slot{border-color:var(--success);background:var(--success-bg);}
.sign-slot.wrong-slot{border-color:var(--error);background:var(--error-bg);}
.term-chip{
  padding:6px 12px;border-radius:20px;font-size:13px;font-weight:600;
  background:var(--primary);color:#fff;cursor:pointer;border:none;
  display:inline-flex;align-items:center;min-height:34px;
  touch-action:manipulation;-webkit-tap-highlight-color:transparent;transition:all .12s;
}
.term-chip:active{transform:scale(.96);}
.term-chip.selected-chip{background:var(--primary-dark);outline:3px solid color-mix(in srgb,var(--primary-light) 50%,transparent);}
.term-chip.placed-chip{background:var(--muted-light);cursor:pointer;}
.term-chip.correct-chip{background:var(--success);cursor:default;}
.term-chip.wrong-chip{background:var(--error);cursor:default;}

/* ── Freetext ── */
.freetext-wrap{display:flex;flex-direction:column;gap:8px;}
.freetext-input{
  width:100%;padding:13px 14px;border-radius:var(--radius-sm);
  border:2px solid var(--border);font-size:15px;font-family:inherit;
  -webkit-appearance:none;transition:border-color .15s;
  background:var(--card);color:var(--text);
}
.freetext-input:focus{outline:none;border-color:var(--primary);}
.freetext-input.ans-ok{border-color:var(--success);background:var(--success-bg);}
.freetext-input.ans-fail{border-color:var(--error);background:var(--error-bg);}
.correct-ans-box{
  background:var(--success-bg);border:1px solid var(--success-light);
  border-radius:var(--radius-sm);padding:10px 13px;font-size:13px;display:none;
}
.correct-ans-box.show{display:block;}
.correct-ans-box strong{color:var(--success);}

/* ── Summary ── */
.summary{
  background:var(--card);border-radius:var(--radius);box-shadow:var(--shadow);
  padding:20px;margin:12px;display:none;
  animation:slideInFwd .25s ease;
}
.summary.show{display:block;}
.summary h2{font-size:18px;font-weight:700;margin-bottom:4px;}
.score-big{font-size:52px;font-weight:800;margin:14px 0 2px;letter-spacing:-.02em;}
.score-big.good{color:var(--success);}
.score-big.bad{color:var(--error);}
.score-label{color:var(--muted);font-size:14px;margin-bottom:18px;}
.sum-actions{display:flex;gap:10px;flex-wrap:wrap;margin-bottom:12px;}
.sum-list{border-top:1px solid var(--border);padding-top:12px;}
.sum-item{
  display:flex;align-items:flex-start;gap:10px;
  padding:9px 0;border-bottom:1px solid var(--border);font-size:13px;
  border-radius:6px;transition:background .12s;
}
@media(hover:hover){.sum-item:hover{background:color-mix(in srgb,var(--primary-light) 8%,var(--card));padding-left:6px;}}
.sum-item:last-child{border-bottom:none;}
.si-icon{font-size:16px;flex-shrink:0;margin-top:1px;}
.si-info{flex:1;min-width:0;}
.si-q{font-weight:600;color:var(--text);overflow-wrap:break-word;}
.si-ans{color:var(--muted);margin-top:2px;overflow-wrap:break-word;}
.si-correct{color:var(--success);font-weight:600;}