/* =========================================================================
   AP CALC PREP — design tokens
   Concept: the digital equivalent of an official exam booklet + scoring
   sheet. Ink navy on paper, a mechanical-pencil amber for attention states,
   scantron-style filled ovals as the recurring navigation motif, and a
   printed "verified" stamp seal to signal answer-key rigor.
   ========================================================================= */

@import url('https://fonts.googleapis.com/css2?family=Spectral:ital,wght@0,500;0,600;0,700;1,500&family=IBM+Plex+Sans:wght@400;500;600;700&family=IBM+Plex+Mono:wght@400;500;600&display=swap');

:root{
  --ink:        #16213a;
  --ink-soft:   #3c4863;
  --paper:      #eeece4;
  --paper-raised:#f7f6f1;
  --rule:       #cac6b6;
  --rule-strong:#a8a38f;
  --amber:      #d98e2b;
  --amber-deep: #a8641a;
  --teal:       #2f6e62;
  --teal-deep:  #1f4b43;
  --red:        #b23a2e;
  --red-deep:   #8a2b21;

  --font-display: 'Spectral', Georgia, 'Times New Roman', serif;
  --font-body: 'IBM Plex Sans', -apple-system, Segoe UI, sans-serif;
  --font-mono: 'IBM Plex Mono', 'Courier New', monospace;

  --radius: 3px;
  --shadow-card: 0 1px 0 var(--rule), 0 8px 24px -18px rgba(22,33,58,0.35);
}

*{ box-sizing: border-box; }
html{ -webkit-text-size-adjust: 100%; }
body{
  margin:0;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--font-body);
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
}
a{ color: inherit; }
button{ font-family: inherit; }
:focus-visible{ outline: 3px solid var(--amber); outline-offset: 2px; }

/* faint graph-paper texture used behind hero / booklet cover */
.grid-texture{
  background-image:
    linear-gradient(var(--rule) 1px, transparent 1px),
    linear-gradient(90deg, var(--rule) 1px, transparent 1px);
  background-size: 28px 28px;
  background-position: -1px -1px;
  opacity: 0.35;
}

.wrap{ max-width: 980px; margin: 0 auto; padding: 0 24px; }

/* ---------------------------------------------------------------------
   Top bar
   --------------------------------------------------------------------- */
.topbar{
  border-bottom: 1px solid var(--rule-strong);
  background: var(--paper-raised);
}
.topbar .wrap{
  display:flex; align-items:center; justify-content:space-between;
  padding-top:14px; padding-bottom:14px;
}
.brand{
  display:flex; align-items:baseline; gap:10px;
  font-family: var(--font-display);
  font-weight:700; font-size:1.15rem; letter-spacing:0.01em;
  text-decoration:none; color:var(--ink);
}
.brand .brand-mark{
  display:inline-flex; align-items:center; justify-content:center;
  width:28px; height:28px; border-radius:50%;
  background: var(--ink); color: var(--paper-raised);
  font-family: var(--font-mono); font-size:0.72rem; font-weight:600;
}
.topbar nav{ font-family: var(--font-mono); font-size:0.8rem; color: var(--ink-soft); }

/* ---------------------------------------------------------------------
   Hero / booklet cover
   --------------------------------------------------------------------- */
.cover{
  position:relative;
  border-bottom: 1px solid var(--rule-strong);
  overflow:hidden;
}
.cover-inner{ position:relative; padding: 56px 0 44px; }
.cover-eyebrow{
  font-family: var(--font-mono);
  font-size: 0.74rem;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--ink-soft);
  display:flex; align-items:center; gap:10px;
  margin-bottom:18px;
}
.cover-eyebrow::before{ content:""; width:22px; height:1px; background: var(--rule-strong); }

.cover h1{
  font-family: var(--font-display);
  font-weight:700;
  font-size: clamp(2.1rem, 4.4vw, 3.4rem);
  line-height:1.05;
  margin: 0 0 14px;
  max-width: 15ch;
}
.cover p.lede{
  max-width: 54ch;
  font-size: 1.05rem;
  color: var(--ink-soft);
  margin: 0 0 30px;
}

.stamp{
  position:absolute; top:44px; right:0;
  width:118px; height:118px;
}
.stamp svg{ width:100%; height:100%; }
.stamp-text{ font-family: var(--font-mono); font-size:8.6px; letter-spacing:0.06em; fill: var(--teal-deep); }
.stamp-center{ font-family: var(--font-display); font-weight:700; font-size:15px; fill: var(--teal-deep); }

.cta-row{ display:flex; flex-wrap:wrap; gap:12px; align-items:center; }

.btn{
  display:inline-flex; align-items:center; gap:8px;
  font-family: var(--font-body); font-weight:600; font-size:0.95rem;
  padding: 12px 20px;
  border-radius: var(--radius);
  border: 1px solid transparent;
  cursor:pointer;
  text-decoration:none;
  transition: transform .12s ease, box-shadow .12s ease;
}
.btn:active{ transform: translateY(1px); }
.btn-primary{ background: var(--ink); color: var(--paper-raised); }
.btn-primary:hover{ background:#0f1830; }
.btn-secondary{ background: transparent; color: var(--ink); border-color: var(--rule-strong); }
.btn-secondary:hover{ background: var(--paper-raised); }
.btn-amber{ background: var(--amber); color:#241503; }
.btn-amber:hover{ background: var(--amber-deep); color:#fff; }
.btn[disabled]{ opacity:0.45; cursor:not-allowed; }
.btn-sm{ padding:8px 14px; font-size:0.85rem; }

/* ---------------------------------------------------------------------
   Stat strip
   --------------------------------------------------------------------- */
.stat-strip{
  display:grid; grid-template-columns: repeat(4, 1fr);
  border-top:1px solid var(--rule); border-bottom:1px solid var(--rule);
  background: var(--paper-raised);
}
.stat-strip div{
  padding: 18px 20px;
  border-right: 1px solid var(--rule);
}
.stat-strip div:last-child{ border-right:none; }
.stat-num{ font-family: var(--font-mono); font-weight:600; font-size:1.5rem; color: var(--ink); display:block; }
.stat-label{ font-size:0.78rem; color: var(--ink-soft); }

/* ---------------------------------------------------------------------
   Section headers
   --------------------------------------------------------------------- */
.section{ padding: 48px 0; }
.section-head{ margin-bottom:26px; }
.section-head .kicker{
  font-family: var(--font-mono); font-size:0.72rem; letter-spacing:0.12em;
  text-transform:uppercase; color: var(--amber-deep); display:block; margin-bottom:8px;
}
.section-head h2{
  font-family: var(--font-display); font-weight:700; font-size:1.7rem; margin:0 0 8px;
}
.section-head p{ color: var(--ink-soft); max-width:60ch; margin:0; }

/* ---------------------------------------------------------------------
   Module + mode cards
   --------------------------------------------------------------------- */
.card-grid{ display:grid; grid-template-columns: 1fr 1fr; gap:18px; }
@media (max-width: 720px){ .card-grid{ grid-template-columns: 1fr; } .stat-strip{ grid-template-columns: 1fr 1fr; } }

.mode-card{
  background: var(--paper-raised);
  border:1px solid var(--rule);
  border-radius: var(--radius);
  padding: 24px;
  box-shadow: var(--shadow-card);
  display:flex; flex-direction:column; gap:12px;
}
.mode-card h3{ font-family: var(--font-display); font-size:1.25rem; margin:0; }
.mode-card p{ color: var(--ink-soft); margin:0; font-size:0.93rem; flex:1; }
.mode-meta{ display:flex; gap:14px; font-family: var(--font-mono); font-size:0.76rem; color: var(--ink-soft); flex-wrap:wrap; }
.mode-meta span{ display:flex; align-items:center; gap:6px; }
.dot{ width:6px; height:6px; border-radius:50%; background: var(--amber); display:inline-block; }

.unit-list{ display:grid; grid-template-columns: repeat(2, 1fr); gap:10px; margin-top:6px; }
@media (max-width:560px){ .unit-list{ grid-template-columns: 1fr; } }
.unit-row{
  display:flex; align-items:center; justify-content:space-between;
  padding:10px 12px; border:1px solid var(--rule); border-radius: var(--radius);
  background: var(--paper-raised); cursor:pointer; font-size:0.88rem;
}
.unit-row:hover{ border-color: var(--rule-strong); }
.unit-row .u-num{ font-family: var(--font-mono); color: var(--ink-soft); margin-right:8px; }
.unit-row .u-count{ font-family: var(--font-mono); font-size:0.76rem; color: var(--ink-soft); }

footer.site-footer{
  border-top:1px solid var(--rule);
  padding: 26px 0 40px;
  color: var(--ink-soft);
  font-size:0.82rem;
}

/* =========================================================================
   EXAM ENGINE (exam.html)
   ========================================================================= */
.exam-shell{ min-height:100vh; display:flex; flex-direction:column; }

.exam-topbar{
  position: sticky; top:0; z-index:20;
  background: var(--ink); color: var(--paper-raised);
  border-bottom: 3px solid var(--amber);
}
.exam-topbar .wrap{ display:flex; align-items:center; justify-content:space-between; padding:10px 24px; max-width:1080px; }
.exam-title{ font-family: var(--font-mono); font-size:0.82rem; letter-spacing:0.04em; }
.exam-title b{ color: var(--amber); }
.timer{
  font-family: var(--font-mono); font-weight:600; font-size:1.05rem;
  display:flex; align-items:center; gap:8px;
  padding:4px 12px; border-radius: var(--radius); background: rgba(255,255,255,0.08);
}
.timer.low{ background: var(--red); color:#fff; animation: pulse 1s infinite; }
@keyframes pulse{ 0%,100%{opacity:1;} 50%{opacity:0.55;} }
.no-calc-banner{
  background: var(--red-deep); color:#fff; font-family: var(--font-mono);
  font-size:0.75rem; letter-spacing:0.06em; text-align:center; padding:5px;
}
.calc-banner{
  background: var(--teal-deep); color:#fff; font-family: var(--font-mono);
  font-size:0.75rem; letter-spacing:0.06em; text-align:center; padding:5px;
}

.exam-body{ flex:1; display:flex; max-width:1080px; margin:0 auto; width:100%; }
.exam-main{ flex:1; padding: 30px 28px 100px; min-width:0; }
.exam-side{
  width:230px; border-left:1px solid var(--rule); padding: 30px 18px;
  background: var(--paper-raised);
}
@media (max-width: 860px){
  .exam-body{ flex-direction:column; }
  .exam-side{ width:auto; border-left:none; border-top:1px solid var(--rule); order:2; }
}

.q-meta{
  font-family: var(--font-mono); font-size:0.78rem; color: var(--ink-soft);
  display:flex; justify-content:space-between; align-items:center; margin-bottom:18px;
}
.flag-btn{
  display:inline-flex; align-items:center; gap:6px; cursor:pointer; user-select:none;
  border:1px solid var(--rule-strong); background:var(--paper-raised); border-radius:var(--radius);
  padding:6px 10px; font-family: var(--font-mono); font-size:0.76rem;
}
.flag-btn.active{ background: var(--amber); border-color: var(--amber-deep); color:#241503; }

.q-stem{ font-size:1.12rem; line-height:1.6; margin-bottom:22px; }
.choices{ display:flex; flex-direction:column; gap:10px; }
.choice{
  display:flex; align-items:flex-start; gap:12px; cursor:pointer;
  padding:12px 14px; border:1px solid var(--rule); border-radius: var(--radius);
  background: var(--paper-raised);
}
.choice:hover{ border-color: var(--ink-soft); }
.choice input{ margin-top:4px; accent-color: var(--ink); }
.choice .bubble{
  flex:0 0 auto; width:26px; height:26px; border-radius:50%;
  border:1.5px solid var(--ink-soft); display:flex; align-items:center; justify-content:center;
  font-family: var(--font-mono); font-size:0.78rem; color: var(--ink-soft);
}
.choice.selected .bubble{ background: var(--ink); border-color: var(--ink); color:#fff; }
.choice.selected{ border-color: var(--ink); background:#e8e5da; }
.choice .c-text{ padding-top:2px; }

.choice.correct{ border-color: var(--teal); background:#e6f0ec; }
.choice.correct .bubble{ background: var(--teal); border-color: var(--teal-deep); color:#fff; }
.choice.incorrect{ border-color: var(--red); background:#f6e9e7; }
.choice.incorrect .bubble{ background: var(--red); border-color: var(--red-deep); color:#fff; }

.exam-nav-buttons{ display:flex; justify-content:space-between; margin-top:28px; gap:10px; }

.qnav-title{ font-family: var(--font-mono); font-size:0.72rem; letter-spacing:0.1em; text-transform:uppercase; color:var(--ink-soft); margin-bottom:10px; }
.qnav-grid{ display:grid; grid-template-columns: repeat(5, 1fr); gap:6px; }
.qnav-dot{
  width:100%; aspect-ratio:1; border-radius:50%; border:1.5px solid var(--rule-strong);
  display:flex; align-items:center; justify-content:center;
  font-family: var(--font-mono); font-size:0.72rem; cursor:pointer; background: var(--paper-raised);
}
.qnav-dot.answered{ background: var(--ink); color:#fff; border-color: var(--ink); }
.qnav-dot.flagged{ border-color: var(--amber-deep); box-shadow: 0 0 0 2px var(--amber) inset; }
.qnav-dot.current{ outline:2px solid var(--amber); outline-offset:2px; }
.qnav-legend{ margin-top:14px; font-size:0.74rem; color: var(--ink-soft); display:flex; flex-direction:column; gap:6px; }
.qnav-legend span{ display:flex; align-items:center; gap:8px; }
.legend-dot{ width:12px; height:12px; border-radius:50%; border:1.5px solid var(--rule-strong); display:inline-block; }

.frq-textarea{
  width:100%; min-height:220px; font-family: var(--font-mono); font-size:0.92rem;
  padding:14px; border:1px solid var(--rule-strong); border-radius: var(--radius);
  background: var(--paper-raised); color: var(--ink); resize:vertical;
}
.frq-part{ margin-bottom:26px; padding-bottom:22px; border-bottom:1px dashed var(--rule); }
.frq-part:last-child{ border-bottom:none; }
.frq-solution{
  margin-top:14px; padding:16px; background:#eef3f1; border:1px solid var(--teal); border-radius: var(--radius);
  display:none;
}
.frq-solution.shown{ display:block; }
.frq-solution .label{ font-family: var(--font-mono); font-size:0.74rem; text-transform:uppercase; letter-spacing:0.08em; color: var(--teal-deep); margin-bottom:8px; display:block; }

/* ---------------------------------------------------------------------
   Instructions / modal-like full screens
   --------------------------------------------------------------------- */
.instructions-screen{ max-width:720px; margin:0 auto; padding: 60px 24px 80px; }
.instructions-screen h1{ font-family: var(--font-display); font-size:1.9rem; margin-bottom:6px; }
.instructions-screen .sub{ color:var(--ink-soft); font-family: var(--font-mono); font-size:0.85rem; margin-bottom:28px; }
.instructions-box{
  background: var(--paper-raised); border:1px solid var(--rule); border-radius: var(--radius);
  padding:22px 24px; margin-bottom:20px;
}
.instructions-box h3{ font-family: var(--font-display); margin-top:0; }
.instructions-box ul{ padding-left:20px; margin:10px 0 0; }
.instructions-box li{ margin-bottom:6px; }

/* ---------------------------------------------------------------------
   Results screen
   --------------------------------------------------------------------- */
.score-hero{
  display:flex; gap:34px; align-items:center; flex-wrap:wrap;
  padding: 32px 0; border-bottom:1px solid var(--rule-strong);
}
.score-ring{ position:relative; width:140px; height:140px; flex:0 0 auto; }
.score-ring svg{ transform: rotate(-90deg); }
.score-ring .num{
  position:absolute; inset:0; display:flex; flex-direction:column; align-items:center; justify-content:center;
  font-family: var(--font-mono);
}
.score-ring .num b{ font-size:1.7rem; }
.score-ring .num span{ font-size:0.7rem; color: var(--ink-soft); }

.ap-score-table{ display:flex; gap:8px; margin-top:14px; }
.ap-score-chip{
  font-family: var(--font-mono); font-size:0.82rem; padding:6px 10px; border:1px solid var(--rule-strong);
  border-radius: var(--radius);
}
.ap-score-chip.current{ background: var(--ink); color:#fff; border-color:var(--ink); }

.breakdown-table{ width:100%; border-collapse:collapse; margin-top:10px; }
.breakdown-table th, .breakdown-table td{
  text-align:left; padding:9px 10px; border-bottom:1px solid var(--rule); font-size:0.88rem;
}
.breakdown-table th{ font-family: var(--font-mono); font-size:0.72rem; text-transform:uppercase; letter-spacing:0.06em; color:var(--ink-soft); }
.bar-cell{ width:160px; }
.bar-track{ height:8px; background: var(--rule); border-radius:4px; overflow:hidden; }
.bar-fill{ height:100%; background: var(--teal); }

.review-item{
  border:1px solid var(--rule); border-radius: var(--radius); margin-bottom:14px; overflow:hidden;
  background: var(--paper-raised);
}
.review-item-head{
  display:flex; justify-content:space-between; align-items:center; padding:12px 16px; cursor:pointer;
  font-family: var(--font-mono); font-size:0.82rem;
}
.review-item-head .status-correct{ color: var(--teal-deep); }
.review-item-head .status-incorrect{ color: var(--red-deep); }
.review-item-head .status-skipped{ color: var(--ink-soft); }
.review-item-body{ padding:0 16px 18px; display:none; }
.review-item-body.open{ display:block; }
.explain-box{ margin-top:14px; padding:12px 14px; border-radius:var(--radius); font-size:0.9rem; }
.explain-box.ok{ background:#e6f0ec; border:1px solid var(--teal); }
.explain-box.why-wrong{ background:#f6e9e7; border:1px solid var(--red); margin-top:8px; }

.filter-row{ display:flex; gap:8px; margin: 18px 0; flex-wrap:wrap; }
.chip-toggle{
  font-family: var(--font-mono); font-size:0.78rem; padding:7px 12px; border-radius: 999px;
  border:1px solid var(--rule-strong); background: var(--paper-raised); cursor:pointer;
}
.chip-toggle.active{ background: var(--ink); color:#fff; border-color: var(--ink); }

.katex-display{ margin: 0.6em 0 !important; }

@media print{
  .exam-topbar, .exam-side, .btn{ display:none !important; }
}

/* ---------------------------------------------------------------------
   Subject hub (top-level index.html)
   --------------------------------------------------------------------- */
.subject-grid{ display:grid; grid-template-columns: repeat(2, 1fr); gap:18px; margin-top:6px; }
@media (max-width:720px){ .subject-grid{ grid-template-columns: 1fr; } }
.subject-card{
  display:flex; flex-direction:column; gap:10px;
  background: var(--paper-raised); border:1px solid var(--rule); border-radius: var(--radius);
  padding:22px; box-shadow: var(--shadow-card); text-decoration:none; color:var(--ink);
  transition: transform .12s ease, border-color .12s ease;
}
.subject-card:hover{ border-color: var(--ink-soft); transform: translateY(-1px); }
.subject-card .sc-top{ display:flex; align-items:center; gap:12px; }
.subject-card .sc-mark{
  width:38px; height:38px; border-radius:50%; background:var(--ink); color:var(--paper-raised);
  display:flex; align-items:center; justify-content:center; font-family:var(--font-mono); font-size:1.05rem; flex:0 0 auto;
}
.subject-card h3{ font-family: var(--font-display); font-size:1.15rem; margin:0; }
.subject-card .sc-group{ font-family: var(--font-mono); font-size:0.7rem; text-transform:uppercase; letter-spacing:0.1em; color:var(--amber-deep); }
.subject-card p{ color: var(--ink-soft); font-size:0.9rem; margin:0; }
.subject-card .sc-status{ font-family: var(--font-mono); font-size:0.74rem; color: var(--ink-soft); margin-top:auto; padding-top:6px; border-top:1px dashed var(--rule); }

/* ---------------------------------------------------------------------
   Adaptive difficulty + hardened/progressive scoring UI
   --------------------------------------------------------------------- */
.adaptive-tag{
  display:inline-block; font-family: var(--font-mono); font-size:0.68rem; text-transform:uppercase;
  letter-spacing:0.06em; background: var(--amber); color:#241503; padding:2px 7px; border-radius:20px;
}
.diff-tag{
  display:inline-block; font-family: var(--font-mono); font-size:0.68rem; text-transform:uppercase;
  letter-spacing:0.04em; padding:1px 7px; border-radius:20px; border:1px solid var(--rule);
}
.diff-tag.diff-easy{ background:#e6f0ec; border-color:var(--teal); color:#1f4d43; }
.diff-tag.diff-medium{ background:#fbeed9; border-color:var(--amber-deep); color:#7a4a06; }
.diff-tag.diff-hard{ background:#f6e9e7; border-color:var(--red); color:#7a2318; }

.certify-note{
  max-width:46ch; font-size:0.85rem; margin-top:10px; padding:10px 12px;
  background:#fbeed9; border:1px solid var(--amber-deep); border-radius:var(--radius); color:#5a3a05;
}

.history-bars{ display:flex; flex-direction:column; gap:8px; margin-top:14px; }
.history-bar-row{ display:flex; align-items:center; gap:10px; }
.history-bar-track{
  flex:1 1 auto; height:10px; border-radius:6px; background:#e5e1d2; overflow:hidden;
}
.history-bar-fill{ height:100%; background: var(--teal); border-radius:6px; }
.history-bar-fill.current{ background: var(--ink); }
.history-bar-label{
  font-family: var(--font-mono); font-size:0.78rem; color: var(--ink-soft); width:56px; text-align:right; flex:0 0 auto;
}