:root {
  font-family: Inter, ui-sans-serif, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  color: #162033;
  background: #f4f7fb;
  --navy: #0b2f5b;
  --blue: #1456a0;
  --teal: #0b8f91;
  --teal-soft: #e9f7f6;
  --ink: #162033;
  --muted: #66758b;
  --line: #dce4ee;
  --card: #ffffff;
  --bg: #f4f7fb;
  --success: #167552;
  --success-soft: #edf8f2;
  --danger: #b8414c;
  --danger-soft: #fff0f2;
  --amber: #946400;
  --amber-soft: #fff6d9;
  --shadow: 0 16px 42px rgba(17, 41, 72, 0.08);
}

* { box-sizing: border-box; }
html, body { margin: 0; min-height: 100%; background: var(--bg); color: var(--ink); }
body { min-width: 320px; }
button, input, textarea { font: inherit; }
button, a { -webkit-tap-highlight-color: transparent; }
button:focus-visible, a:focus-visible, textarea:focus-visible { outline: 3px solid rgba(20, 86, 160, .28); outline-offset: 2px; }
button { cursor: pointer; }

.app-shell { min-height: 100vh; display: grid; grid-template-columns: 232px minmax(0, 1fr); }
.sidebar { position: sticky; top: 0; height: 100vh; padding: 26px 20px; background: #0b294e; color: #fff; display: flex; flex-direction: column; z-index: 20; }
.brand { display: flex; align-items: center; gap: 11px; text-decoration: none; color: #fff; }
.brand-mark { width: 38px; height: 38px; border-radius: 12px; display: grid; place-items: center; background: linear-gradient(145deg, #0f7895, #0a4f7d); font-weight: 900; font-size: 19px; }
.brand-title { font-size: 21px; font-weight: 900; letter-spacing: -.03em; }
.brand-sub { color: #b8c9dd; font-size: 10px; margin-top: 2px; }
.dev-pill { display: inline-flex; margin-top: 20px; width: fit-content; padding: 6px 9px; border: 1px solid rgba(255,255,255,.16); border-radius: 999px; color: #ffe7a0; background: rgba(255, 214, 89, .08); font-size: 9px; font-weight: 850; letter-spacing: .07em; text-transform: uppercase; }
.side-nav { margin-top: 32px; display: grid; gap: 8px; }
.side-link { display: flex; align-items: center; gap: 11px; min-height: 44px; padding: 0 12px; color: #c5d5e7; text-decoration: none; border-radius: 11px; font-size: 13px; font-weight: 700; }
.side-link:hover { background: rgba(255,255,255,.06); color: #fff; }
.side-link.active { background: #fff; color: #0b294e; }
.side-icon { width: 22px; text-align: center; font-size: 17px; }
.side-session { margin-top: auto; padding-top: 24px; }
.side-session strong { display: block; font-size: 12px; }
.side-session small { display: block; color: #9db3ca; margin-top: 4px; line-height: 1.45; }
.side-progress { height: 6px; margin-top: 12px; border-radius: 99px; background: rgba(255,255,255,.12); overflow: hidden; }
.side-progress > span { display: block; height: 100%; background: #32b8b1; border-radius: inherit; }

.mobile-header { display: none; }
.mobile-nav { display: none; }
.main-shell { min-width: 0; }
.topbar { height: 66px; padding: 0 30px; border-bottom: 1px solid rgba(220,228,238,.9); background: rgba(244,247,251,.92); backdrop-filter: blur(16px); display: flex; align-items: center; gap: 16px; position: sticky; top: 0; z-index: 15; }
.topbar-title { font-size: 14px; font-weight: 850; }
.topbar-sub { color: var(--muted); font-size: 11px; }
.topbar-actions { margin-left: auto; display: flex; gap: 9px; }
.icon-btn { min-width: 40px; height: 40px; border: 1px solid var(--line); background: #fff; color: var(--navy); border-radius: 11px; }

.page { width: min(1440px, 100%); margin: 0 auto; padding: 30px 34px 48px; }
.page-head { display: flex; align-items: flex-end; justify-content: space-between; gap: 24px; margin-bottom: 24px; }
.eyebrow { color: var(--teal); font-size: 10px; text-transform: uppercase; letter-spacing: .11em; font-weight: 900; }
h1 { margin: 7px 0 0; color: #10213a; font-size: clamp(28px, 3vw, 44px); line-height: 1.05; letter-spacing: -.045em; }
.page-head p { max-width: 600px; margin: 9px 0 0; color: var(--muted); font-size: 13px; line-height: 1.6; }

.notice { margin-bottom: 18px; padding: 12px 14px; border: 1px solid #ecd89a; background: var(--amber-soft); color: #6d500d; border-radius: 13px; font-size: 11px; line-height: 1.5; }
.card { background: var(--card); border: 1px solid var(--line); border-radius: 18px; box-shadow: 0 1px 0 rgba(17,41,72,.02); }
.card-pad { padding: 20px; }
.muted { color: var(--muted); }

.home-grid { display: grid; grid-template-columns: minmax(0, 1.5fr) minmax(300px, .75fr); gap: 18px; align-items: start; }
.hero-card { padding: 28px; min-height: 320px; background: linear-gradient(145deg, #ffffff 0%, #f1f7fb 100%); }
.hero-card h2 { margin: 10px 0 10px; font-size: clamp(26px, 3vw, 40px); line-height: 1.08; letter-spacing: -.04em; }
.hero-card p { color: var(--muted); line-height: 1.65; max-width: 680px; font-size: 13px; }
.hero-actions { margin-top: 24px; display: flex; flex-wrap: wrap; gap: 10px; }
.primary-btn, .secondary-btn { min-height: 46px; padding: 0 17px; border-radius: 12px; font-weight: 850; font-size: 12px; text-decoration: none; display: inline-flex; align-items: center; justify-content: center; border: 0; }
.primary-btn { color: #fff; background: linear-gradient(135deg, #1456a0, #0b8f91); }
.secondary-btn { color: #17304d; background: #fff; border: 1px solid var(--line); }
.metric-row { display: grid; grid-template-columns: repeat(3, 1fr); gap: 12px; margin-top: 24px; }
.metric { padding: 14px; border-radius: 14px; background: rgba(255,255,255,.76); border: 1px solid #e1e9f1; }
.metric b { display: block; font-size: 22px; }
.metric span { display: block; color: var(--muted); font-size: 10px; margin-top: 3px; }
.focus-list { display: grid; gap: 10px; }
.focus-card { padding: 15px; display: grid; grid-template-columns: 1fr auto; gap: 14px; align-items: center; }
.focus-card b { display: block; font-size: 12px; }
.focus-card small { display: block; color: var(--muted); margin-top: 4px; }
.mastery { font-size: 11px; font-weight: 900; color: var(--danger); }
.section-label { margin: 26px 0 11px; font-size: 11px; font-weight: 900; color: #52637a; text-transform: uppercase; letter-spacing: .08em; }
.question-list { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 10px; }
.question-list a { text-decoration: none; color: inherit; }
.question-tile { padding: 15px; min-height: 100px; transition: transform .15s ease, border-color .15s ease; }
.question-tile:hover { transform: translateY(-1px); border-color: #b9c9dd; }
.question-tile-top { display: flex; justify-content: space-between; gap: 12px; }
.question-tile b { font-size: 12px; }
.question-tile p { margin: 9px 0 0; color: var(--muted); font-size: 11px; line-height: 1.45; }
.tag { display: inline-flex; align-items: center; min-height: 24px; padding: 0 8px; border-radius: 999px; background: #edf4fb; color: #22598e; font-size: 9px; font-weight: 850; white-space: nowrap; }
.tag.teal { background: var(--teal-soft); color: #0d7779; }
.tag.warn { background: var(--amber-soft); color: var(--amber); }

.study-grid { display: grid; grid-template-columns: 190px minmax(520px, 760px) minmax(280px, 360px); gap: 18px; justify-content: center; align-items: start; }
.session-rail, .context-pane { position: sticky; top: 86px; }
.session-rail { padding: 15px; }
.rail-title { font-size: 11px; font-weight: 900; }
.rail-progress { color: var(--muted); font-size: 10px; margin-top: 4px; }
.navigator { margin-top: 14px; display: grid; grid-template-columns: repeat(5, 1fr); gap: 6px; }
.nav-dot { aspect-ratio: 1; border-radius: 8px; border: 1px solid var(--line); background: #fff; color: #5f6e82; font-size: 9px; font-weight: 850; }
.nav-dot.current { border-color: var(--blue); color: var(--blue); background: #edf4fb; }
.nav-dot.done { background: var(--success-soft); color: var(--success); border-color: #b7dfcc; }

.question-card { padding: 25px; }
.question-meta { display: flex; flex-wrap: wrap; gap: 7px; align-items: center; }
.question-index { margin-left: auto; color: var(--muted); font-size: 10px; }
.question-stem { margin: 24px 0 20px; font-size: clamp(18px, 1.6vw, 23px); line-height: 1.55; font-weight: 760; letter-spacing: -.015em; }
.statement-reason { padding: 14px; border-radius: 13px; background: #f7f9fc; margin-bottom: 16px; }
.statement-reason b { display: block; font-size: 10px; color: #52637a; margin-bottom: 5px; }
.statement-reason p { margin: 0 0 13px; font-size: 13px; line-height: 1.55; }
.answer-list { display: grid; gap: 10px; }
.answer-option { width: 100%; text-align: left; display: grid; grid-template-columns: 34px 1fr; gap: 12px; align-items: start; padding: 13px; border: 1px solid var(--line); background: #fff; color: var(--ink); border-radius: 13px; min-height: 54px; }
.answer-option:hover { border-color: #aebed2; }
.answer-option.selected { background: #eef8f8; border-color: #58b7b2; box-shadow: inset 0 0 0 1px rgba(11,143,145,.1); }
.answer-letter { width: 30px; height: 30px; border-radius: 9px; background: #f0f3f7; display: grid; place-items: center; font-weight: 900; font-size: 11px; }
.answer-option.selected .answer-letter { background: var(--teal); color: #fff; }
.answer-copy { font-size: 13px; line-height: 1.5; padding-top: 4px; }
.tf-row { border: 1px solid var(--line); border-radius: 13px; padding: 13px; }
.tf-copy { display: grid; grid-template-columns: 26px 1fr; gap: 8px; font-size: 13px; line-height: 1.48; }
.tf-controls { display: grid; grid-template-columns: 1fr 1fr; gap: 8px; margin-top: 10px; }
.tf-controls button { min-height: 40px; border-radius: 10px; border: 1px solid var(--line); background: #f8fafc; color: #56677d; font-weight: 800; }
.tf-controls button.on-true { background: var(--success-soft); color: var(--success); border-color: #a7d7bf; }
.tf-controls button.on-false { background: var(--danger-soft); color: var(--danger); border-color: #e8a8b0; }
.question-footer { display: flex; justify-content: space-between; gap: 12px; align-items: center; margin-top: 18px; }
.submit-btn { min-width: 150px; min-height: 46px; border: 0; border-radius: 12px; color: #fff; background: linear-gradient(135deg, #1456a0, #0b8f91); font-weight: 900; }
.submit-btn:disabled { opacity: .4; cursor: not-allowed; }

.context-pane { padding: 16px; display: grid; gap: 14px; }
.context-block + .context-block { padding-top: 14px; border-top: 1px solid var(--line); }
.context-label { font-size: 9px; font-weight: 900; text-transform: uppercase; letter-spacing: .09em; color: #718096; }
.context-value { margin-top: 5px; font-size: 21px; font-weight: 900; color: #17304d; }
.confidence { display: grid; grid-template-columns: repeat(5, 1fr); gap: 6px; margin-top: 9px; }
.confidence button { aspect-ratio: 1; border-radius: 999px; border: 1px solid var(--line); background: #fff; font-size: 10px; color: #52637a; font-weight: 850; }
.confidence button.active { background: var(--teal); color: #fff; border-color: var(--teal); }
.context-help { margin-top: 7px; color: var(--muted); font-size: 9px; line-height: 1.4; }
.shortcut-list { display: grid; gap: 6px; margin-top: 8px; }
.shortcut { display: flex; justify-content: space-between; color: var(--muted); font-size: 9px; }
kbd { border: 1px solid var(--line); background: #f7f9fb; border-bottom-width: 2px; border-radius: 5px; padding: 2px 5px; color: #41536a; }

.explanation-grid { display: grid; grid-template-columns: minmax(0, 1.4fr) minmax(320px, .72fr); gap: 18px; align-items: start; }
.explanation-main { padding: 24px; }
.correct-banner { padding: 15px; border: 1px solid #a9d7c1; background: var(--success-soft); border-radius: 14px; }
.correct-banner.wrong { border-color: #e4a8b0; background: var(--danger-soft); }
.correct-banner small { display: block; color: var(--muted); font-size: 9px; }
.correct-banner b { display: block; margin-top: 4px; font-size: 15px; }
.explanation-main h2 { margin: 23px 0 9px; font-size: 16px; }
.explanation-main p { color: #42536a; line-height: 1.65; font-size: 13px; }
.rationale-list { display: grid; gap: 8px; margin-top: 12px; }
.rationale { display: grid; grid-template-columns: 31px 1fr; gap: 10px; padding: 12px; border: 1px solid var(--line); border-radius: 12px; }
.rationale.correct { border-color: #a9d7c1; background: #f4fbf7; }
.rationale .answer-letter { width: 27px; height: 27px; }
.rationale b { display: block; font-size: 11px; }
.rationale span { display: block; margin-top: 3px; color: var(--muted); font-size: 10px; line-height: 1.45; }
.support-stack { display: grid; gap: 12px; }
.evidence-card, .notes-card, .concept-card { padding: 18px; }
.evidence-item { margin-top: 12px; padding: 12px; border-radius: 11px; background: #f5f8fb; }
.evidence-item b { font-size: 11px; display: block; }
.evidence-item span { font-size: 9px; display: block; color: var(--muted); margin-top: 3px; line-height: 1.45; }
.dev-source { display: inline-flex; margin-top: 8px; color: var(--amber); background: var(--amber-soft); padding: 4px 7px; border-radius: 999px; font-size: 8px; font-weight: 850; }
.notes-card textarea { width: 100%; min-height: 130px; resize: vertical; border: 1px solid var(--line); border-radius: 11px; padding: 11px; margin-top: 10px; color: var(--ink); background: #fbfcfe; line-height: 1.5; }
.save-note { margin-top: 8px; min-height: 38px; padding: 0 12px; border: 1px solid var(--line); border-radius: 10px; background: #fff; color: var(--blue); font-weight: 800; font-size: 10px; }

.review-layout { display: grid; grid-template-columns: minmax(0, 1fr) 360px; gap: 18px; align-items: start; }
.review-summary { display: grid; grid-template-columns: repeat(4, 1fr); gap: 10px; margin-bottom: 14px; }
.summary-box { padding: 14px; }
.summary-box b { display: block; font-size: 22px; }
.summary-box span { display: block; font-size: 9px; color: var(--muted); margin-top: 3px; }
.review-list { display: grid; gap: 10px; }
.review-item { padding: 15px; display: grid; grid-template-columns: 1fr auto; gap: 14px; }
.review-item h3 { margin: 5px 0 0; font-size: 13px; line-height: 1.4; }
.review-item p { margin: 7px 0 0; color: var(--muted); font-size: 10px; line-height: 1.45; }
.review-actions { display: flex; flex-direction: column; gap: 7px; align-items: flex-end; }
.retry { text-decoration: none; color: #fff; background: var(--blue); border-radius: 9px; padding: 9px 11px; font-size: 9px; font-weight: 850; }
.weak-tags { display: flex; flex-wrap: wrap; gap: 6px; margin-top: 9px; }

.notes-layout { display: grid; grid-template-columns: minmax(0, 1.15fr) minmax(320px, .85fr); gap: 18px; align-items: start; }
.map-title { font-size: 16px; font-weight: 900; }
.map-root { margin: 18px auto; width: fit-content; padding: 12px 16px; background: var(--navy); color: #fff; border-radius: 11px; font-weight: 850; font-size: 12px; }
.map-branches { display: grid; grid-template-columns: repeat(auto-fit, minmax(135px, 1fr)); gap: 10px; position: relative; }
.map-node { padding: 13px; border: 1px solid #a8ced0; background: #f0fbfa; border-radius: 12px; text-align: center; }
.map-node b { display: block; font-size: 11px; color: #0d6f73; }
.map-node span { display: block; color: var(--muted); font-size: 9px; line-height: 1.4; margin-top: 4px; }

@media (max-width: 1199px) {
  .app-shell { grid-template-columns: 78px minmax(0, 1fr); }
  .sidebar { padding: 22px 12px; align-items: center; }
  .brand-copy, .dev-pill, .side-link span:not(.side-icon), .side-session { display: none; }
  .side-nav { width: 100%; }
  .side-link { justify-content: center; padding: 0; }
  .study-grid { grid-template-columns: minmax(0, 1fr) minmax(270px, 320px); }
  .session-rail { display: none; }
  .page { padding-left: 24px; padding-right: 24px; }
  .home-grid { grid-template-columns: 1fr; }
  .question-list { grid-template-columns: repeat(2, 1fr); }
  .review-layout { grid-template-columns: 1fr; }
  .review-side { display: none; }
}

@media (max-width: 900px) {
  .study-grid, .explanation-grid, .notes-layout { grid-template-columns: 1fr; }
  .context-pane, .support-stack { position: static; }
  .context-pane { grid-template-columns: repeat(3, 1fr); }
  .context-block + .context-block { padding-top: 0; border-top: 0; border-left: 1px solid var(--line); padding-left: 14px; }
  .support-stack { grid-template-columns: 1fr 1fr; }
}

@media (max-width: 767px) {
  .app-shell { display: block; }
  .sidebar, .topbar { display: none; }
  .mobile-header { position: sticky; top: 0; z-index: 30; display: flex; align-items: center; height: 58px; padding: 0 16px; border-bottom: 1px solid rgba(220,228,238,.9); background: rgba(250,252,254,.96); backdrop-filter: blur(14px); }
  .mobile-header .brand { color: var(--navy); gap: 8px; }
  .mobile-header .brand-mark { width: 31px; height: 31px; border-radius: 9px; font-size: 15px; color: #fff; }
  .mobile-header .brand-title { font-size: 17px; }
  .mobile-dev { margin-left: auto; font-size: 8px; color: var(--amber); font-weight: 850; }
  .mobile-nav { position: fixed; left: 0; right: 0; bottom: 0; z-index: 40; height: calc(66px + env(safe-area-inset-bottom)); padding-bottom: env(safe-area-inset-bottom); display: grid; grid-template-columns: repeat(4, 1fr); background: rgba(255,255,255,.97); border-top: 1px solid var(--line); backdrop-filter: blur(16px); }
  .mobile-nav a { text-decoration: none; color: #7a8798; display: grid; place-items: center; align-content: center; gap: 3px; font-size: 9px; font-weight: 750; }
  .mobile-nav a.active { color: var(--blue); }
  .mobile-nav .side-icon { font-size: 17px; }
  .page { padding: 20px 14px calc(86px + env(safe-area-inset-bottom)); }
  .page-head { align-items: flex-start; flex-direction: column; margin-bottom: 17px; }
  .page-head h1 { font-size: 30px; }
  .hero-card { padding: 20px; min-height: auto; }
  .hero-card h2 { font-size: 28px; }
  .metric-row { grid-template-columns: repeat(3, 1fr); }
  .question-list { grid-template-columns: 1fr; }
  .study-grid { display: block; }
  .question-card { padding: 18px; }
  .question-stem { font-size: 18px; margin-top: 18px; }
  .context-pane { margin-top: 12px; position: static; grid-template-columns: 1fr 1fr; }
  .context-block:last-child { display: none; }
  .question-footer { align-items: stretch; flex-direction: column-reverse; }
  .submit-btn { width: 100%; }
  .explanation-main, .evidence-card, .notes-card, .concept-card { padding: 17px; }
  .support-stack { grid-template-columns: 1fr; }
  .review-summary { grid-template-columns: repeat(2, 1fr); }
  .review-item { grid-template-columns: 1fr; }
  .review-actions { align-items: stretch; }
  .retry { text-align: center; }
  .map-branches { grid-template-columns: 1fr 1fr; }
}

@media (max-width: 430px) {
  .metric-row { grid-template-columns: 1fr; }
  .context-pane { grid-template-columns: 1fr; }
  .context-block + .context-block { border-left: 0; border-top: 1px solid var(--line); padding-left: 0; padding-top: 12px; }
  .map-branches { grid-template-columns: 1fr; }
}