*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --bg:         #0d1117;
  --surface:    #161b22;
  --surface-2:  #21262d;
  --surface-3:  #30363d;
  --border:     #30363d;
  --primary:    #818cf8;
  --primary-d:  #6366f1;
  --primary-bg: rgba(129,140,248,.12);
  --success:    #34d399;
  --success-bg: rgba(52,211,153,.12);
  --danger:     #f87171;
  --danger-bg:  rgba(248,113,113,.12);
  --fire:       #fbbf24;
  --fire-bg:    rgba(251,191,36,.1);
  --purple:     #c084fc;
  --text:       #e6edf3;
  --muted:      #8b949e;
  --subtle:     #6e7681;
  --r-sm:  8px;
  --r:    12px;
  --r-lg: 18px;
  --ease: .2s ease;
}

html, body { height: 100%; }
body {
  font-family: 'Inter', -apple-system, sans-serif;
  background: var(--bg);
  color: var(--text);
  font-size: 15px;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

/* ── Screens ───────────────────────────────────────── */
.screen { display: none; width: 100%; min-height: 100vh; }

/* Centered screens */
#subject-screen.active,
#setup-screen.active,
#score-screen.active {
  display: flex;
  align-items: center;
  justify-content: center;
}

/* Quiz screen is full-page block */
#quiz-screen.active { display: block; }

.screen-inner { width: 100%; max-width: 640px; padding: 3rem 1.5rem; }

/* ── Subject Screen ────────────────────────────────── */
.brand { text-align: center; margin-bottom: 2.5rem; }
.brand-icon { font-size: 3rem; margin-bottom: .5rem; }
.brand-name {
  font-size: 2.75rem; font-weight: 800; letter-spacing: -.04em;
  background: linear-gradient(135deg, var(--primary), var(--purple));
  -webkit-background-clip: text; -webkit-text-fill-color: transparent; background-clip: text;
}
.brand-sub { color: var(--muted); margin-top: .35rem; font-size: .95rem; }

.subject-grid { display: flex; flex-direction: column; gap: .75rem; }
.subject-card {
  display: flex; align-items: center; gap: 1rem;
  padding: 1.25rem 1.5rem;
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--r-lg); cursor: pointer; text-align: left;
  color: var(--text); transition: all var(--ease); width: 100%;
}
.subject-card:hover {
  border-color: var(--primary); background: var(--surface-2);
  transform: translateY(-2px); box-shadow: 0 8px 24px rgba(129,140,248,.15);
}
.subject-icon { font-size: 2rem; flex-shrink: 0; }
.subject-info { flex: 1; }
.subject-name { display: block; font-size: 1rem; font-weight: 600; }
.subject-meta { display: block; font-size: .8rem; color: var(--muted); margin-top: .1rem; }
.subject-arrow { color: var(--muted); font-size: 1.1rem; flex-shrink: 0; }

/* ── Setup Screen ──────────────────────────────────── */
.setup-inner { max-width: 680px; }
.setup-header { display: flex; align-items: center; gap: 1rem; margin-bottom: 1.5rem; }
.back-btn {
  background: transparent; border: 1px solid var(--border);
  color: var(--muted); padding: .4rem .85rem; border-radius: var(--r-sm);
  cursor: pointer; font-size: .82rem; font-family: inherit; transition: all var(--ease);
}
.back-btn:hover { border-color: var(--muted); color: var(--text); }
.setup-title { font-size: 1.45rem; font-weight: 700; letter-spacing: -.02em; }

.setup-grid { display: grid; grid-template-columns: 1fr 1fr; gap: .85rem; margin-bottom: 1.25rem; }
.span-2 { grid-column: span 2; }

.setup-card {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--r-lg); padding: 1.2rem 1.3rem;
}
.setup-label {
  display: block; font-size: .72rem; font-weight: 600;
  text-transform: uppercase; letter-spacing: .07em;
  color: var(--muted); margin-bottom: .8rem;
}

.mode-row { display: grid; grid-template-columns: repeat(3, 1fr); gap: .6rem; }
.mode-btn {
  display: flex; align-items: center; gap: .75rem;
  padding: .85rem 1rem; background: var(--surface-2);
  border: 1px solid var(--border); border-radius: var(--r);
  cursor: pointer; color: var(--text); font-family: inherit;
  text-align: left; transition: all var(--ease);
}
.mode-btn:hover { border-color: var(--primary); background: var(--primary-bg); }
.mode-btn.active { border-color: var(--primary); background: var(--primary-bg); box-shadow: 0 0 0 1px var(--primary) inset; }
.mode-icon { font-size: 1.4rem; flex-shrink: 0; }
.mode-name { font-size: .88rem; font-weight: 600; line-height: 1.2; }
.mode-desc { font-size: .73rem; color: var(--muted); }

.lecture-grid { display: grid; grid-template-columns: repeat(4, 1fr); gap: .35rem; }
.lec-btn {
  padding: .45rem .2rem; background: var(--surface-2);
  border: 1px solid var(--border); border-radius: var(--r-sm);
  color: var(--muted); font-size: .78rem; font-weight: 500;
  cursor: pointer; font-family: inherit; transition: all var(--ease);
}
.lec-btn:hover { border-color: var(--primary); color: var(--text); }
.lec-btn.active { background: var(--primary-bg); border-color: var(--primary); color: var(--primary); font-weight: 600; }

.count-presets { display: flex; flex-wrap: wrap; gap: .35rem; margin-bottom: .7rem; }
.count-btn {
  padding: .4rem .75rem; background: var(--surface-2);
  border: 1px solid var(--border); border-radius: var(--r-sm);
  color: var(--muted); font-size: .82rem; font-weight: 500;
  cursor: pointer; font-family: inherit; transition: all var(--ease);
}
.count-btn:hover { border-color: var(--primary); color: var(--text); }
.count-btn.active { background: var(--primary-bg); border-color: var(--primary); color: var(--primary); font-weight: 600; }

.custom-row { display: flex; align-items: center; gap: .6rem; }
.custom-label { font-size: .78rem; color: var(--muted); white-space: nowrap; }
.custom-input {
  flex: 1; padding: .4rem .65rem; background: var(--surface-2);
  border: 1px solid var(--border); border-radius: var(--r-sm);
  color: var(--text); font-size: .82rem; font-family: inherit; outline: none;
  transition: border-color var(--ease);
}
.custom-input:focus { border-color: var(--primary); }
.custom-input::placeholder { color: var(--subtle); }

.toggles-row { display: flex; gap: 2rem; flex-wrap: wrap; }
.toggle-item {
  display: flex; align-items: center; gap: .6rem;
  cursor: pointer; user-select: none; flex: 1; min-width: 160px;
}
.toggle-icon { font-size: 1rem; }
.toggle-text { font-size: .88rem; color: var(--text); flex: 1; }

.switch { position: relative; width: 38px; height: 21px; flex-shrink: 0; }
.switch input { opacity: 0; width: 0; height: 0; position: absolute; }
.knob {
  position: absolute; inset: 0; background: var(--surface-3);
  border-radius: 99px; cursor: pointer; transition: background var(--ease);
}
.knob::before {
  content: ''; position: absolute; top: 3px; left: 3px;
  width: 15px; height: 15px; background: var(--muted);
  border-radius: 50%; transition: all var(--ease);
}
.switch input:checked + .knob { background: var(--primary-d); }
.switch input:checked + .knob::before { transform: translateX(17px); background: white; }

.start-btn {
  width: 100%; display: flex; align-items: center; justify-content: center; gap: .5rem;
  padding: .95rem 2rem; background: var(--primary-d); border: none;
  border-radius: var(--r); color: white; font-size: 1rem; font-weight: 600;
  font-family: inherit; cursor: pointer; transition: all var(--ease);
  box-shadow: 0 4px 20px rgba(99,102,241,.35);
}
.start-btn:hover { background: #4338ca; transform: translateY(-1px); box-shadow: 0 6px 28px rgba(99,102,241,.5); }
.start-btn:active { transform: none; }

/* ── Quiz Screen ───────────────────────────────────── */
.quiz-wrap {
  max-width: 700px; margin: 0 auto;
  padding: 0 1.5rem; display: flex; flex-direction: column; min-height: 100vh;
}

.quiz-header {
  position: sticky; top: 0; z-index: 10;
  background: var(--bg); padding: 1.1rem 0 .75rem;
  border-bottom: 1px solid var(--border);
}
.quiz-top {
  display: flex; align-items: center; justify-content: space-between;
  margin-bottom: .65rem;
}
.quit-btn {
  padding: .3rem .75rem; background: transparent;
  border: 1px solid var(--border); border-radius: var(--r-sm);
  color: var(--subtle); font-size: .78rem; font-family: inherit;
  cursor: pointer; transition: all var(--ease);
}
.quit-btn:hover { border-color: var(--danger); color: var(--danger); }

.quiz-chips { display: flex; align-items: center; gap: .35rem; }
.chip {
  padding: .28rem .7rem; background: var(--surface);
  border: 1px solid var(--border); border-radius: 99px;
  font-size: .78rem; font-weight: 500; color: var(--muted);
}
.chip-primary { color: var(--primary); border-color: rgba(129,140,248,.3); background: var(--primary-bg); }
.chip-fire    { color: var(--fire);    border-color: rgba(251,191,36,.3);   background: var(--fire-bg); }

.icon-btn {
  display: flex; align-items: center; justify-content: center;
  width: 32px; height: 32px; background: transparent;
  border: 1px solid var(--border); border-radius: var(--r-sm);
  color: var(--muted); cursor: pointer; font-size: .82rem;
  font-family: inherit; transition: all var(--ease);
}
.icon-btn:hover { border-color: var(--muted); color: var(--text); }
.icon-btn.bookmarked { border-color: var(--fire); color: var(--fire); background: var(--fire-bg); }
.icon-btn.bookmarked svg { fill: var(--fire); }

.progress-track { height: 3px; background: var(--surface-2); border-radius: 99px; overflow: hidden; }
.progress-fill {
  height: 100%; width: 0%;
  background: linear-gradient(90deg, var(--primary-d), var(--primary));
  border-radius: 99px; transition: width .4s ease;
}

.quiz-body { flex: 1; padding: 1.75rem 0 2.5rem; display: flex; flex-direction: column; gap: 1rem; }

.question-card {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--r-lg); padding: 1.5rem;
}
.question-meta { display: flex; align-items: center; justify-content: space-between; margin-bottom: .85rem; }
.badge {
  font-size: .7rem; font-weight: 600; text-transform: uppercase; letter-spacing: .06em;
  color: var(--primary); background: var(--primary-bg); padding: .22rem .6rem; border-radius: 99px;
}
.q-counter { font-size: .78rem; font-weight: 600; color: var(--subtle); }
.q-text { font-size: 1.08rem; font-weight: 500; line-height: 1.65; color: var(--text); }

/* Options */
.options-container { display: flex; flex-direction: column; gap: .55rem; }
.option-btn {
  display: flex; align-items: flex-start; gap: .85rem; width: 100%;
  padding: .9rem 1.15rem; background: var(--surface);
  border: 1px solid var(--border); border-radius: var(--r);
  color: var(--text); font-size: .93rem; font-family: inherit;
  cursor: pointer; text-align: left; transition: all var(--ease); line-height: 1.5;
}
.option-btn:hover:not(:disabled) { border-color: var(--primary); background: var(--primary-bg); }
.option-btn:disabled { cursor: default; }
.opt-letter {
  display: inline-flex; align-items: center; justify-content: center;
  width: 25px; height: 25px; min-width: 25px; border-radius: 6px;
  background: var(--surface-2); border: 1px solid var(--border);
  font-size: .75rem; font-weight: 700; color: var(--muted); flex-shrink: 0; margin-top: 1px;
  transition: all var(--ease);
}
.option-btn:hover:not(:disabled) .opt-letter { background: var(--primary-bg); border-color: var(--primary); color: var(--primary); }
.option-btn.correct { border-color: var(--success); background: var(--success-bg); }
.option-btn.correct .opt-letter { background: var(--success); border-color: var(--success); color: #0d1117; }
.option-btn.wrong { border-color: var(--danger); background: var(--danger-bg); color: var(--muted); }
.option-btn.wrong .opt-letter { background: var(--danger); border-color: var(--danger); color: white; }

/* Answer area (flashcard) */
.answer-area {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--r); overflow: hidden;
}
.answer-area:empty { display: none; }
.show-answer-btn {
  width: 100%; padding: .9rem 1.25rem; background: transparent; border: none;
  color: var(--primary); font-size: .92rem; font-weight: 600;
  font-family: inherit; cursor: pointer; transition: all var(--ease);
  display: block;
}
.show-answer-btn:hover { background: var(--primary-bg); }
.answer-reveal {
  padding: 1.1rem 1.35rem; border-top: 1px solid var(--border);
  font-size: .92rem; line-height: 1.75; color: var(--text);
}
.self-assess-row {
  display: flex; gap: .5rem; margin-top: .85rem;
  padding-top: .85rem; border-top: 1px solid var(--border);
}
.sa-btn {
  flex: 1; padding: .55rem; border-radius: var(--r-sm);
  font-size: .82rem; font-weight: 600; font-family: inherit;
  cursor: pointer; border: 1px solid; transition: all var(--ease);
}
.sa-btn:disabled { opacity: .5; cursor: default; }
.sa-btn.yes { border-color: var(--success); color: var(--success); background: var(--success-bg); }
.sa-btn.yes:hover:not(:disabled) { background: var(--success); color: #0d1117; }
.sa-btn.no  { border-color: var(--danger);  color: var(--danger);  background: var(--danger-bg); }
.sa-btn.no:hover:not(:disabled)  { background: var(--danger); color: white; }

/* ── Slide Viewer ──────────────────────────────────── */
.slide-panel {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--r-lg); overflow: hidden;
}
.slide-panel-head {
  display: flex; align-items: center; justify-content: space-between;
  padding: .8rem 1rem; border-bottom: 1px solid var(--border);
}
.slide-info-text { font-size: .8rem; font-weight: 600; color: var(--muted); }

.slide-canvas-wrap {
  background: #fff; position: relative;
  min-height: 100px; display: flex; align-items: center; justify-content: center;
  overflow: hidden;
}
.slide-loading {
  padding: 2rem; color: #666; font-size: .85rem; text-align: center;
}
#slide-canvas { display: block; width: 100%; height: auto; }

.slide-nav {
  display: flex; align-items: center; justify-content: space-between;
  padding: .65rem .9rem; border-top: 1px solid var(--border); gap: .5rem;
}
.slide-nav-btn {
  padding: .38rem .8rem; background: var(--surface-2);
  border: 1px solid var(--border); border-radius: var(--r-sm);
  color: var(--muted); font-size: .78rem; font-family: inherit;
  cursor: pointer; transition: all var(--ease); white-space: nowrap;
}
.slide-nav-btn:hover:not(:disabled) { border-color: var(--primary); color: var(--primary); }
.slide-nav-btn:disabled { opacity: .35; cursor: default; }
.slide-page-ctrl {
  display: flex; align-items: center; gap: .4rem;
  flex: 1; justify-content: center;
}
.slide-page-input {
  width: 52px; padding: .32rem .5rem; text-align: center;
  background: var(--surface-2); border: 1px solid var(--border);
  border-radius: var(--r-sm); color: var(--text); font-size: .8rem;
  font-family: inherit; outline: none; transition: border-color var(--ease);
}
.slide-page-input:focus { border-color: var(--primary); }
.slide-total { font-size: .78rem; color: var(--muted); }

/* Footer */
.quiz-footer {
  display: flex; align-items: center; gap: .6rem; flex-wrap: wrap;
  padding-top: .25rem;
}
.ai-btn, .slides-btn {
  display: flex; align-items: center; gap: .45rem;
  padding: .6rem 1rem; background: var(--surface);
  border: 1px solid var(--border); border-radius: var(--r);
  color: var(--muted); font-size: .82rem; font-weight: 500;
  font-family: inherit; cursor: pointer; transition: all var(--ease);
}
.ai-btn:hover     { border-color: var(--purple); color: var(--purple); background: rgba(192,132,252,.08); }
.slides-btn:hover { border-color: var(--primary); color: var(--primary); background: var(--primary-bg); }
.slides-btn.active { border-color: var(--primary); color: var(--primary); background: var(--primary-bg); }

.kbd-hint { flex: 1; font-size: .71rem; color: var(--subtle); text-align: center; min-width: 0; }
.kbd { display: inline-block; padding: .1em .38em; background: var(--surface-2); border: 1px solid var(--border); border-radius: 4px; font-family: monospace; font-size: .85em; }

.next-btn {
  display: none; align-items: center; gap: .45rem; margin-left: auto;
  padding: .6rem 1.35rem; background: var(--primary-d); border: none;
  border-radius: var(--r); color: white; font-size: .9rem; font-weight: 600;
  font-family: inherit; cursor: pointer; transition: all var(--ease);
}
.next-btn.visible { display: flex; }
.next-btn:hover { background: #4338ca; transform: translateX(2px); }

/* ── AI Panel ──────────────────────────────────────── */
.ai-overlay {
  display: none; position: fixed; inset: 0;
  background: rgba(0,0,0,.55); backdrop-filter: blur(2px); z-index: 40;
}
.ai-overlay.open { display: block; }
.ai-panel {
  position: fixed; right: 0; top: 0; bottom: 0; width: 420px; max-width: 92vw;
  background: var(--surface); border-left: 1px solid var(--border);
  display: flex; flex-direction: column; z-index: 50;
  transform: translateX(100%); transition: transform .3s cubic-bezier(.4,0,.2,1);
  box-shadow: -8px 0 48px rgba(0,0,0,.5);
}
.ai-panel.open { transform: translateX(0); }
.ai-header {
  display: flex; align-items: center; justify-content: space-between;
  padding: 1.1rem 1.4rem; border-bottom: 1px solid var(--border);
}
.ai-title { display: flex; align-items: center; gap: .6rem; font-weight: 600; font-size: .92rem; }
.ai-dot {
  width: 8px; height: 8px; border-radius: 50%;
  background: var(--purple); box-shadow: 0 0 8px var(--purple);
  animation: pulse 2s ease-in-out infinite;
}
@keyframes pulse { 0%,100% { opacity: 1; } 50% { opacity: .35; } }
.ai-response { flex: 1; overflow-y: auto; padding: 1.4rem; font-size: .88rem; line-height: 1.75; color: var(--text); }
.ai-loading {
  display: flex; flex-direction: column; align-items: center;
  justify-content: center; height: 100%; gap: 1rem; color: var(--muted);
}
.ai-dots { display: flex; gap: .4rem; }
.ai-dots span {
  width: 8px; height: 8px; border-radius: 50%; background: var(--purple);
  animation: bdot 1.2s ease-in-out infinite;
}
.ai-dots span:nth-child(2) { animation-delay: .2s; }
.ai-dots span:nth-child(3) { animation-delay: .4s; }
@keyframes bdot { 0%,80%,100% { transform: translateY(0); } 40% { transform: translateY(-7px); } }
.ai-content h2 { font-size: 1rem; font-weight: 700; color: var(--purple); margin: 1.1rem 0 .4rem; }
.ai-content h3 { font-size: .92rem; font-weight: 700; color: var(--primary); margin: .9rem 0 .35rem; }
.ai-content p { margin-bottom: .65rem; }
.ai-content ul, .ai-content ol { padding-left: 1.4rem; margin-bottom: .65rem; }
.ai-content li { margin-bottom: .25rem; }
.ai-content strong { color: var(--text); font-weight: 600; }
.ai-content code {
  background: var(--surface-2); border: 1px solid var(--border); border-radius: 4px;
  padding: .1em .35em; font-size: .84em; font-family: monospace; color: var(--purple);
}
.ai-content pre {
  background: var(--surface-2); border: 1px solid var(--border);
  border-radius: var(--r-sm); padding: .9rem; overflow-x: auto; margin-bottom: .65rem;
}
.ai-content pre code { background: none; border: none; padding: 0; }

/* ── Score Screen ──────────────────────────────────── */
.score-inner { text-align: center; max-width: 480px; }
.score-trophy { font-size: 4rem; margin-bottom: .75rem; }
.score-title { font-size: 1.6rem; font-weight: 800; letter-spacing: -.02em; margin-bottom: .4rem; }
.score-pct {
  font-size: 5.5rem; font-weight: 800; letter-spacing: -.05em; line-height: 1;
  background: linear-gradient(135deg, var(--primary), var(--purple));
  -webkit-background-clip: text; -webkit-text-fill-color: transparent; background-clip: text;
  margin: .4rem 0 .3rem;
}
.score-sub { color: var(--muted); margin-bottom: 1.5rem; }
.score-breakdown {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--r-lg); padding: 1.1rem; margin-bottom: 1.5rem;
  display: grid; grid-template-columns: repeat(3,1fr); gap: .75rem; text-align: center;
}
.bd-label { font-size: .72rem; color: var(--muted); text-transform: uppercase; letter-spacing: .06em; margin-bottom: .25rem; }
.bd-val { font-size: 1.6rem; font-weight: 700; }
.bd-val.ok  { color: var(--success); }
.bd-val.bad { color: var(--danger); }
.score-actions { display: flex; flex-direction: column; gap: .55rem; margin-bottom: 1.75rem; }
.btn-primary {
  width: 100%; padding: .82rem; background: var(--primary-d); border: none;
  border-radius: var(--r); color: white; font-size: .92rem; font-weight: 600;
  font-family: inherit; cursor: pointer; transition: background var(--ease);
}
.btn-primary:hover { background: #4338ca; }
.btn-primary.sm { width: auto; padding: .55rem 1.4rem; }
.btn-secondary {
  width: 100%; padding: .82rem; background: var(--surface);
  border: 1px solid var(--border); border-radius: var(--r);
  color: var(--text); font-size: .92rem; font-weight: 500;
  font-family: inherit; cursor: pointer; transition: all var(--ease);
}
.btn-secondary:hover { border-color: var(--primary); background: var(--primary-bg); }
.btn-ghost {
  width: 100%; padding: .82rem; background: transparent;
  border: 1px solid var(--border); border-radius: var(--r);
  color: var(--muted); font-size: .92rem; font-family: inherit;
  cursor: pointer; transition: all var(--ease);
}
.btn-ghost:hover { border-color: var(--muted); color: var(--text); }
.bookmarks-section {
  text-align: left; background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--r-lg); padding: 1.2rem;
}
.bookmarks-heading { font-size: .88rem; font-weight: 600; margin-bottom: .7rem; }
.bookmarks-list { display: flex; flex-direction: column; gap: .4rem; }
.bookmark-item {
  background: var(--surface-2); border: 1px solid var(--border);
  border-radius: var(--r-sm); padding: .65rem .85rem;
  font-size: .82rem; color: var(--muted); line-height: 1.5;
}

/* ── Modals ────────────────────────────────────────── */
.modal-bg {
  display: none; position: fixed; inset: 0;
  background: rgba(0,0,0,.7); backdrop-filter: blur(4px);
  z-index: 100; align-items: center; justify-content: center;
}
.modal-bg.open { display: flex; }
.modal-box {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--r-lg); width: 100%; max-width: 420px; margin: 1rem;
  box-shadow: 0 8px 48px rgba(0,0,0,.6);
  animation: modal-in .2s ease;
}
@keyframes modal-in { from { opacity: 0; transform: scale(.95) translateY(8px); } to { opacity: 1; transform: none; } }
.modal-head {
  display: flex; align-items: center; justify-content: space-between;
  padding: 1.1rem 1.4rem; border-bottom: 1px solid var(--border);
  font-size: .95rem; font-weight: 600;
}
.modal-body { padding: 1.4rem; }
.modal-foot {
  padding: .9rem 1.4rem; border-top: 1px solid var(--border);
  display: flex; justify-content: flex-end;
}
.err-text { color: var(--muted); font-size: .9rem; line-height: 1.6; }

/* ── KaTeX (inherit dark theme colours) ───────────── */
.katex { color: inherit !important; font-size: 1em; }
.katex-display { overflow-x: auto; overflow-y: hidden; padding: .25rem 0; }

/* ── Scrollbar ─────────────────────────────────────── */
::-webkit-scrollbar { width: 5px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--surface-3); border-radius: 3px; }
::-webkit-scrollbar-thumb:hover { background: var(--subtle); }

/* ── Formula Practice ─────────────────────────────── */
#fp-select-screen.active,
#fp-drill-screen.active { display: flex; align-items: flex-start; justify-content: center; }

.fp-select-inner, .fp-drill-inner { max-width: 680px; }

.fp-intro { color: var(--muted); font-size: .9rem; margin-bottom: 1.5rem; }

/* Category sections */
.fp-categories { display: flex; flex-direction: column; gap: 1.5rem; }
.fp-category-title {
  font-size: .72rem; font-weight: 700; text-transform: uppercase;
  letter-spacing: .08em; color: var(--subtle); margin-bottom: .6rem;
}
.fp-formula-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(180px, 1fr)); gap: .6rem; }

.fp-formula-btn {
  display: flex; flex-direction: column; gap: .3rem;
  padding: .9rem 1rem; background: var(--surface);
  border: 1px solid var(--border); border-radius: var(--r);
  color: var(--text); font-family: inherit;
  cursor: pointer; text-align: left; transition: all var(--ease);
}
.fp-formula-btn:hover {
  border-color: var(--primary); background: var(--primary-bg);
  transform: translateY(-1px);
}
.fp-formula-btn-name { font-size: .88rem; font-weight: 600; }
.fp-formula-btn-hint { font-size: .74rem; color: var(--muted); line-height: 1.4; }

/* Drill screen */
.fp-drill-header {
  display: flex; align-items: center; gap: .85rem;
  margin-bottom: 1.25rem; flex-wrap: wrap;
}
.fp-drill-title-group { flex: 1; min-width: 0; }
.fp-drill-title-group .setup-title { margin-bottom: .15rem; }
.fp-stats-chip {
  font-size: .75rem; font-weight: 600;
  color: var(--success); background: var(--success-bg);
  border: 1px solid rgba(52,211,153,.25);
  padding: .22rem .65rem; border-radius: 99px; display: inline-block;
}
.fp-regen-btn {
  padding: .48rem 1rem; background: var(--surface);
  border: 1px solid var(--border); border-radius: var(--r-sm);
  color: var(--muted); font-size: .82rem; font-family: inherit;
  cursor: pointer; transition: all var(--ease); white-space: nowrap;
}
.fp-regen-btn:hover { border-color: var(--primary); color: var(--primary); }

/* Cards */
.fp-card {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--r-lg); padding: 1.25rem 1.4rem;
  margin-bottom: .85rem;
}
.fp-hint-text { font-size: .82rem; color: var(--muted); margin-bottom: .75rem; }
.fp-latex-display { overflow-x: auto; }
.fp-latex-display .katex-display { margin: 0; }

.fp-given-label {
  font-size: .7rem; font-weight: 700; text-transform: uppercase;
  letter-spacing: .07em; color: var(--muted); margin-bottom: .65rem;
}
.fp-vars-row { display: flex; flex-wrap: wrap; gap: .5rem; }
.fp-var-chip {
  display: flex; align-items: center; gap: .5rem;
  padding: .45rem .85rem; background: var(--surface-2);
  border: 1px solid var(--border); border-radius: var(--r-sm);
  font-size: .88rem;
}
.fp-var-name { color: var(--muted); }
.fp-var-eq   { color: var(--subtle); font-size: .78rem; }
.fp-var-val  { font-weight: 700; color: var(--primary); font-variant-numeric: tabular-nums; }

.fp-answer-label {
  display: block; font-size: .8rem; font-weight: 600; color: var(--muted);
  margin-bottom: .6rem;
}
.fp-input-row { display: flex; gap: .5rem; }
.fp-input {
  flex: 1; padding: .65rem .9rem; background: var(--surface-2);
  border: 1px solid var(--border); border-radius: var(--r-sm);
  color: var(--text); font-size: 1rem; font-family: 'Inter', monospace;
  outline: none; transition: border-color var(--ease);
  font-variant-numeric: tabular-nums;
}
.fp-input:focus { border-color: var(--primary); }
.fp-input::placeholder { color: var(--subtle); }
.fp-check-btn {
  padding: .65rem 1.4rem; background: var(--primary-d); border: none;
  border-radius: var(--r-sm); color: white; font-size: .9rem; font-weight: 600;
  font-family: inherit; cursor: pointer; transition: background var(--ease);
  white-space: nowrap;
}
.fp-check-btn:hover { background: #4338ca; }

.fp-feedback {
  margin-top: .85rem; padding: .75rem 1rem;
  border-radius: var(--r-sm); font-size: .9rem; font-weight: 500;
}
.fp-feedback.correct {
  background: var(--success-bg); border: 1px solid rgba(52,211,153,.3); color: var(--success);
}
.fp-feedback.wrong {
  background: var(--danger-bg);  border: 1px solid rgba(248,113,113,.3); color: var(--danger);
}
.fp-feedback .fp-correct-val { font-weight: 700; color: var(--text); }

/* History */
.fp-history { margin-bottom: .85rem; }
.fp-history-label {
  font-size: .72rem; font-weight: 700; text-transform: uppercase;
  letter-spacing: .07em; color: var(--subtle); margin-bottom: .5rem;
}
.fp-history-item {
  display: flex; justify-content: space-between; align-items: center;
  padding: .5rem .75rem; border-radius: var(--r-sm); margin-bottom: .35rem;
  font-size: .8rem; background: var(--surface-2); border: 1px solid var(--border);
}
.fp-history-item.ok  { border-color: rgba(52,211,153,.2); }
.fp-history-item.bad { border-color: rgba(248,113,113,.2); }
.fp-hi-vars  { color: var(--muted); flex: 1; min-width: 0; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.fp-hi-ans   { font-weight: 600; margin-left: .75rem; white-space: nowrap; }
.fp-hi-ans.ok  { color: var(--success); }
.fp-hi-ans.bad { color: var(--danger); }

.fp-footer {
  display: flex; justify-content: flex-start;
  padding: .25rem 0 .5rem;
}

/* ── Responsive ────────────────────────────────────── */
@media (max-width: 580px) {
  .setup-grid { grid-template-columns: 1fr; }
  .span-2 { grid-column: span 1; }
  .mode-row { grid-template-columns: 1fr; }
  .score-breakdown { grid-template-columns: 1fr 1fr; }
  .ai-panel { width: 100%; border-left: none; border-top: 1px solid var(--border); top: auto; border-radius: var(--r-lg) var(--r-lg) 0 0; height: 70vh; }
}