:root {
  color-scheme: light;
  --navy: #102a43;
  --navy-2: #173f6c;
  --blue: #2563eb;
  --blue-dark: #1d4ed8;
  --blue-soft: #eff6ff;
  --teal: #0f766e;
  --teal-soft: #ecfdf5;
  --green: #15803d;
  --green-soft: #f0fdf4;
  --orange: #c2410c;
  --orange-soft: #fff7ed;
  --red: #b91c1c;
  --red-soft: #fef2f2;
  --text: #334155;
  --muted: #64748b;
  --page: #f8fafc;
  --surface: #ffffff;
  --line: #e2e8f0;
  --line-strong: #cbd5e1;
  --shadow: 0 18px 45px rgba(15, 23, 42, 0.09);
  --shadow-small: 0 8px 24px rgba(15, 23, 42, 0.06);
  --radius: 18px;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; scroll-padding-top: 6rem; }
body {
  min-width: 320px;
  margin: 0;
  background: var(--page);
  color: var(--text);
  font: 400 16px/1.65 Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  -webkit-font-smoothing: antialiased;
}
button, input, select { font: inherit; }
button, a { -webkit-tap-highlight-color: transparent; }
a { color: var(--blue); }
canvas { display: block; width: 100%; height: 100%; }
.shell { width: min(1220px, calc(100% - 2.5rem)); margin-inline: auto; }
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 40;
  border-bottom: 1px solid rgba(226, 232, 240, 0.94);
  background: rgba(255, 255, 255, 0.95);
  box-shadow: 0 4px 18px rgba(15, 23, 42, 0.05);
  backdrop-filter: blur(14px);
}
.topbar {
  min-height: 5rem;
  display: grid;
  grid-template-columns: minmax(190px, 1fr) minmax(230px, 360px) auto;
  gap: 1.2rem;
  align-items: center;
}
.brand {
  color: var(--navy);
  font-weight: 850;
  letter-spacing: -0.03em;
  text-decoration: none;
}
.brand span {
  display: block;
  color: var(--muted);
  font-size: 0.7rem;
  font-weight: 650;
  letter-spacing: 0.02em;
}
.header-progress { display: grid; gap: 0.3rem; }
.header-progress > span { color: var(--muted); font-size: 0.75rem; font-weight: 700; }
.progress-track {
  height: 7px;
  overflow: hidden;
  border-radius: 999px;
  background: #e7edf4;
}
.progress-track span {
  display: block;
  width: 0;
  height: 100%;
  border-radius: inherit;
  background: linear-gradient(90deg, var(--blue), #14b8a6);
  transition: width 0.35s ease;
}
.progress-track.large { height: 10px; }

.primary-button,
.outline-button,
.ghost-button,
.choice-button,
.checkpoint-button,
.hint-button {
  display: inline-flex;
  min-height: 46px;
  align-items: center;
  justify-content: center;
  border-radius: 10px;
  cursor: pointer;
  font-weight: 800;
  text-decoration: none;
  transition: transform 0.18s ease, border-color 0.18s ease, background 0.18s ease, color 0.18s ease;
}
.primary-button {
  border: 1px solid var(--navy);
  padding: 0.72rem 1.05rem;
  background: var(--navy);
  color: #fff;
}
.primary-button:hover,
.primary-button:focus-visible { background: var(--navy-2); transform: translateY(-1px); }
.primary-button:disabled { cursor: not-allowed; opacity: 0.5; transform: none; }
.outline-button {
  border: 1px solid var(--line-strong);
  padding: 0.72rem 1.05rem;
  background: #fff;
  color: var(--navy);
}
.outline-button:hover,
.outline-button:focus-visible { border-color: var(--blue); color: var(--blue-dark); }
.outline-button:disabled { cursor: not-allowed; opacity: 0.45; }
.outline-button.compact { min-height: 40px; padding: 0.55rem 0.8rem; font-size: 0.78rem; }
.ghost-button {
  border: 1px solid rgba(255, 255, 255, 0.3);
  padding: 0.72rem 1.05rem;
  background: rgba(255, 255, 255, 0.08);
  color: #fff;
}
.ghost-button:hover,
.ghost-button:focus-visible { background: rgba(255, 255, 255, 0.16); }
.full-width { width: 100%; }
.button-row { display: flex; flex-wrap: wrap; gap: 0.65rem; }

.hero {
  overflow: hidden;
  padding: 5.7rem 0 5rem;
  background:
    radial-gradient(circle at 16% 14%, rgba(96, 165, 250, 0.4), transparent 31%),
    radial-gradient(circle at 85% 75%, rgba(45, 212, 191, 0.18), transparent 28%),
    linear-gradient(135deg, var(--navy), #173f6c 57%, #1d4ed8 150%);
  color: #fff;
}
.hero-grid {
  display: grid;
  grid-template-columns: minmax(0, 1.25fr) minmax(290px, 0.75fr);
  gap: clamp(2rem, 6vw, 5rem);
  align-items: end;
}
.hero-badge {
  display: inline-flex;
  padding: 0.42rem 0.8rem;
  border: 1px solid rgba(255, 255, 255, 0.22);
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.12);
  font-size: 0.78rem;
  font-weight: 750;
}
.hero h1 {
  max-width: 780px;
  margin: 1.2rem 0 1rem;
  font-size: clamp(2.8rem, 7vw, 5.4rem);
  line-height: 1.01;
  letter-spacing: -0.065em;
}
.hero p {
  max-width: 760px;
  margin: 0;
  color: rgba(255, 255, 255, 0.84);
  font-size: clamp(1rem, 2vw, 1.17rem);
}
.hero-actions { display: flex; flex-wrap: wrap; gap: 0.75rem; margin-top: 1.6rem; }
.hero-summary {
  display: grid;
  gap: 0.75rem;
  padding: 1.2rem;
  border: 1px solid rgba(255, 255, 255, 0.18);
  border-radius: 18px;
  background: rgba(255, 255, 255, 0.1);
  backdrop-filter: blur(8px);
}
.hero-summary div {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  padding-bottom: 0.65rem;
  border-bottom: 1px solid rgba(255, 255, 255, 0.14);
}
.hero-summary div:last-child { padding: 0; border: 0; }
.hero-summary span { color: rgba(255, 255, 255, 0.66); font-size: 0.8rem; }
.hero-summary strong { font-size: 0.88rem; text-align: right; }

.lesson-layout {
  display: grid;
  grid-template-columns: 225px minmax(0, 1fr);
  gap: 2rem;
  padding: 3rem 0 6rem;
}
.lesson-nav {
  position: sticky;
  top: 6.4rem;
  align-self: start;
  padding: 1.15rem;
  border: 1px solid var(--line);
  border-radius: 16px;
  background: #fff;
  box-shadow: var(--shadow-small);
}
.lesson-nav > strong {
  display: block;
  margin-bottom: 0.7rem;
  color: var(--navy);
  font-size: 0.78rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}
.lesson-nav a {
  display: block;
  padding: 0.62rem 0.68rem;
  border-radius: 8px;
  color: var(--muted);
  font-size: 0.84rem;
  font-weight: 650;
  text-decoration: none;
}
.lesson-nav a:hover,
.lesson-nav a:focus-visible,
.lesson-nav a.active { background: var(--blue-soft); color: var(--blue-dark); }
.lesson-nav a.completed::after { float: right; color: var(--green); content: "✓"; }
.nav-score {
  margin-top: 1rem;
  padding: 0.8rem;
  border-radius: 10px;
  background: #f8fafc;
}
.nav-score span { display: block; color: var(--muted); font-size: 0.68rem; }
.nav-score strong { display: block; margin-top: 0.2rem; color: var(--navy); }

.document {
  min-width: 0;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: 24px;
  background: #fff;
  box-shadow: var(--shadow);
}
.lesson-section { padding: clamp(2rem, 6vw, 4.3rem); border-bottom: 1px solid var(--line); }
.lesson-section:last-child { border-bottom: 0; }
.chapter {
  margin: 0;
  color: var(--blue);
  font-size: 0.75rem;
  font-weight: 850;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}
.lesson-section h2 {
  max-width: 860px;
  margin: 0.65rem 0 1rem;
  color: var(--navy);
  font-size: clamp(2rem, 4vw, 3.25rem);
  line-height: 1.1;
  letter-spacing: -0.05em;
}
.lead { max-width: 850px; color: var(--muted); font-size: 1.06rem; }
.math { color: var(--navy); font-family: "Cambria Math", "Times New Roman", serif; font-weight: 700; }
.definition {
  margin: 2rem 0;
  padding: 1.2rem 1.35rem;
  border-left: 4px solid var(--blue);
  border-radius: 0 12px 12px 0;
  background: #f8fbff;
}
.definition strong { color: var(--navy); }

.concept-grid {
  display: grid;
  grid-template-columns: 1fr auto 1fr auto 1fr;
  gap: 0.75rem;
  align-items: center;
  margin: 2rem 0;
}
.concept-card {
  min-height: 140px;
  padding: 1.1rem;
  border: 1px solid var(--line);
  border-radius: 14px;
  background: #fff;
}
.concept-card.accent { border-color: #bfdbfe; background: var(--blue-soft); }
.concept-card span { color: var(--muted); font-size: 0.72rem; font-weight: 800; letter-spacing: 0.07em; text-transform: uppercase; }
.concept-card strong { display: block; margin: 0.4rem 0; color: var(--navy); font-size: 1.45rem; }
.concept-card p { margin: 0; color: var(--muted); font-size: 0.88rem; }
.concept-arrow { color: var(--blue); font-size: 1.8rem; font-weight: 800; }

.lab {
  margin: 2rem clamp(-2.7rem, -4vw, -1rem) 2.6rem;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: 20px;
  background: #fff;
  box-shadow: 0 12px 30px rgba(15, 23, 42, 0.07);
}
.lab-head {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 1.25rem 1.5rem;
  border-bottom: 1px solid var(--line);
  background: #fbfdff;
}
.lab-head small {
  display: block;
  color: var(--blue);
  font-size: 0.7rem;
  font-weight: 850;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}
.lab-head h3 { margin: 0.18rem 0 0; color: var(--navy); font-size: 1.2rem; }
.live-indicator {
  display: inline-flex;
  align-items: center;
  gap: 0.48rem;
  color: var(--muted);
  font-size: 0.78rem;
}
.live-indicator::before {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: #10b981;
  box-shadow: 0 0 0 5px rgba(16, 185, 129, 0.12);
  content: "";
}
.score-chip {
  display: inline-flex;
  padding: 0.42rem 0.68rem;
  border-radius: 999px;
  background: var(--blue-soft);
  color: var(--blue-dark);
  font-size: 0.78rem;
  font-weight: 800;
}

.machine-layout {
  display: grid;
  grid-template-columns: minmax(260px, 0.8fr) minmax(300px, 1.2fr);
  gap: 1rem;
  padding: 1.35rem 1.5rem;
}
.control-stack { display: grid; align-content: start; gap: 0.65rem; }
.field-label { color: var(--navy); font-size: 0.82rem; font-weight: 800; }
select,
input[type="number"] {
  width: 100%;
  min-height: 46px;
  border: 1px solid var(--line-strong);
  border-radius: 10px;
  background: #fff;
  color: var(--navy);
  padding: 0.7rem 0.8rem;
}
select:focus,
input:focus,
button:focus-visible,
a:focus-visible { outline: 3px solid rgba(37, 99, 235, 0.2); outline-offset: 2px; }
.machine-result {
  margin-top: 0.55rem;
  padding: 1rem;
  border: 1px solid #bfdbfe;
  border-radius: 12px;
  background: linear-gradient(145deg, #fff, var(--blue-soft));
}
.machine-result span { color: var(--muted); font-size: 0.7rem; font-weight: 800; letter-spacing: 0.07em; text-transform: uppercase; }
.machine-result strong { display: block; margin: 0.25rem 0; color: var(--navy); font-size: 2.25rem; line-height: 1.1; }
.machine-result p { margin: 0; color: var(--muted); font-size: 0.88rem; }
.value-table { width: 100%; border-collapse: collapse; overflow: hidden; border: 1px solid var(--line); border-radius: 12px; }
.value-table caption { padding: 0 0 0.6rem; color: var(--navy); font-weight: 800; text-align: left; }
.value-table th,
.value-table td { padding: 0.67rem 0.8rem; border-bottom: 1px solid var(--line); text-align: center; }
.value-table th { background: #f8fafc; color: var(--muted); font-size: 0.74rem; text-transform: uppercase; }
.value-table tr:last-child td { border-bottom: 0; }
.value-table td:first-child { color: var(--navy); font-weight: 800; }
.practice-box {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(240px, 0.65fr);
  gap: 1rem;
  align-items: end;
  margin: 0 1.5rem 1.5rem;
  padding: 1.1rem;
  border: 1px solid #bfdbfe;
  border-radius: 14px;
  background: var(--blue-soft);
}
.practice-box p { margin: 0.25rem 0 0; color: var(--navy); }
.practice-label {
  color: var(--blue-dark);
  font-size: 0.68rem;
  font-weight: 850;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}
.answer-row { display: grid; grid-template-columns: minmax(0, 1fr) auto; gap: 0.6rem; }
.feedback { min-height: 1.55rem; margin: 0.75rem 0 0; color: var(--navy); font-weight: 700; }
.feedback.correct { color: var(--green); }
.feedback.wrong { color: var(--red); }
.practice-box .feedback { grid-column: 1 / -1; margin: 0; }

.rule-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0.9rem;
  margin: 2rem 0;
}
.rule-card { padding: 1.15rem; border: 1px solid var(--line); border-radius: 14px; }
.rule-card span { color: var(--blue); font-size: 0.7rem; font-weight: 850; letter-spacing: 0.07em; text-transform: uppercase; }
.rule-card strong { display: block; margin: 0.45rem 0; color: var(--navy); }
.rule-card p { margin: 0; color: var(--muted); font-size: 0.88rem; }
.relation-stage { padding: 1.4rem 1.5rem 1.5rem; }
.relation-stage > p:first-child { margin-top: 0; color: var(--muted); }
.relation-pairs {
  display: flex;
  flex-wrap: wrap;
  gap: 0.65rem;
  min-height: 72px;
  align-items: center;
  margin: 1.2rem 0;
}
.relation-pair {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  padding: 0.7rem 0.85rem;
  border: 1px solid var(--line);
  border-radius: 10px;
  background: #f8fafc;
  color: var(--navy);
  font-family: "Cambria Math", serif;
  font-weight: 800;
}
.choice-row { display: grid; grid-template-columns: 1fr 1fr; gap: 0.7rem; }
.choice-button { border: 1px solid var(--line-strong); padding: 0.75rem 1rem; background: #fff; color: var(--navy); }
.choice-button:hover,
.choice-button:focus-visible { border-color: var(--blue); }
.choice-button.correct { border-color: #86efac; background: var(--green-soft); color: #166534; }
.choice-button.wrong { border-color: #fecaca; background: var(--red-soft); color: #991b1b; }

.checkpoint {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  margin-top: 2.3rem;
  padding: 1rem 1.1rem;
  border: 1px solid var(--line);
  border-radius: 14px;
  background: #f8fafc;
}
.checkpoint strong { color: var(--navy); }
.checkpoint p { margin: 0.15rem 0 0; color: var(--muted); font-size: 0.88rem; }
.checkpoint-button { flex: 0 0 auto; border: 1px solid var(--line-strong); padding: 0.68rem 0.85rem; background: #fff; color: var(--navy); font-size: 0.78rem; }
.checkpoint.completed { border-color: #bbf7d0; background: var(--green-soft); }
.checkpoint.completed .checkpoint-button { border-color: #86efac; background: #dcfce7; color: #166534; }

.graph-workspace {
  display: grid;
  grid-template-columns: 260px minmax(0, 1fr);
  min-height: 650px;
}
.graph-controls {
  padding: 1.25rem;
  border-right: 1px solid var(--line);
  background: #fbfdff;
}
.graph-controls select { margin: 0.4rem 0 1rem; }
.range-control {
  padding: 0.85rem 0;
  border-top: 1px solid var(--line);
}
.range-control:first-child { border-top: 0; }
.range-head { display: flex; justify-content: space-between; gap: 1rem; margin-bottom: 0.45rem; color: var(--navy); font-size: 0.82rem; font-weight: 800; }
.range-head output { color: var(--blue-dark); }
input[type="range"] { width: 100%; accent-color: var(--blue); }
.range-help { display: block; margin-top: 0.28rem; color: var(--muted); font-size: 0.68rem; }
.preset-row { display: grid; grid-template-columns: 1fr 1fr; gap: 0.45rem; margin: 0.9rem 0; }
.preset-button { min-height: 38px; border: 1px solid var(--line); border-radius: 8px; background: #fff; color: var(--muted); cursor: pointer; font-size: 0.72rem; font-weight: 750; }
.preset-button:hover { border-color: #bfdbfe; color: var(--blue-dark); }
.graph-panel { min-width: 0; padding: 1.25rem; }
.formula-display {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  justify-content: space-between;
  gap: 0.75rem;
  margin-bottom: 0.85rem;
  padding: 0.85rem 1rem;
  border: 1px solid #bfdbfe;
  border-radius: 12px;
  background: var(--blue-soft);
}
.formula-display span { color: var(--muted); font-size: 0.7rem; font-weight: 850; letter-spacing: 0.07em; text-transform: uppercase; }
.formula-display strong { color: var(--navy); font-family: "Cambria Math", serif; font-size: 1.15rem; }
.canvas-shell {
  position: relative;
  height: 510px;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: 16px;
  background: #fff;
}
.coordinate-readout {
  position: absolute;
  right: 12px;
  bottom: 12px;
  padding: 0.45rem 0.65rem;
  border-radius: 8px;
  background: rgba(16, 42, 67, 0.92);
  color: #fff;
  font-size: 0.72rem;
  font-variant-numeric: tabular-nums;
}
.property-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.65rem;
  margin-top: 0.8rem;
}
.property-card { min-width: 0; padding: 0.82rem; border: 1px solid var(--line); border-radius: 11px; background: #fff; }
.property-card span { display: block; color: var(--muted); font-size: 0.65rem; font-weight: 800; letter-spacing: 0.06em; text-transform: uppercase; }
.property-card strong { display: block; margin-top: 0.28rem; color: var(--navy); font-size: 0.9rem; line-height: 1.35; overflow-wrap: anywhere; }
.insight-callout {
  margin: 1rem 0 2rem;
  padding: 1rem 1.1rem;
  border-left: 4px solid var(--teal);
  border-radius: 0 11px 11px 0;
  background: var(--teal-soft);
  color: #285e57;
}

.transformation-legend { display: flex; flex-wrap: wrap; gap: 1.2rem; margin: 1rem 0 0; color: var(--muted); font-size: 0.82rem; }
.transformation-legend i { display: inline-block; width: 30px; margin-right: 0.4rem; vertical-align: middle; border-top: 3px solid; }
.transformation-legend .target-line { border-top-style: dashed; border-color: var(--orange); }
.transformation-legend .student-line { border-color: var(--blue); }
.transform-layout { display: grid; grid-template-columns: minmax(260px, 0.7fr) minmax(0, 1.3fr); gap: 1rem; padding: 1.25rem 1.5rem 1.5rem; }
.transform-controls { min-width: 0; }
.transform-controls > p { margin-top: 0; color: var(--muted); }
.transform-formula { margin: 0.8rem 0; padding: 0.8rem; border-radius: 10px; background: var(--blue-soft); color: var(--navy); font-family: "Cambria Math", serif; font-weight: 800; }
.transform-canvas-shell { height: 470px; }

.reading-layout { display: grid; grid-template-columns: minmax(0, 1.3fr) minmax(250px, 0.7fr); gap: 1rem; padding: 1.25rem 1.5rem 1.5rem; }
.reading-canvas-shell { height: 470px; }
.question-panel { padding: 1.1rem; border: 1px solid var(--line); border-radius: 14px; background: #fbfdff; }
.question-panel h3 { margin: 0.65rem 0 1rem; color: var(--navy); font-size: 1.3rem; line-height: 1.3; }
.answer-options { display: grid; gap: 0.6rem; }
.option-button { width: 100%; min-height: 46px; padding: 0.72rem 0.85rem; border: 1px solid var(--line-strong); border-radius: 10px; background: #fff; color: var(--navy); cursor: pointer; font-weight: 750; text-align: left; }
.option-button:hover,
.option-button:focus-visible { border-color: var(--blue); }
.option-button.correct { border-color: #86efac; background: var(--green-soft); color: #166534; }
.option-button.wrong { border-color: #fecaca; background: var(--red-soft); color: #991b1b; }
.option-button:disabled { cursor: default; }
.hint-button { min-height: 36px; margin-top: 0.8rem; border: 0; padding: 0; background: transparent; color: var(--blue-dark); font-size: 0.78rem; }
.hint-text { margin: 0.35rem 0 0; padding: 0.75rem; border-radius: 9px; background: var(--orange-soft); color: var(--orange); font-size: 0.84rem; }

.model-card {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(280px, 0.8fr);
  gap: 1rem;
  margin: 2rem 0 1rem;
  padding: 1.4rem;
  border: 1px solid var(--line);
  border-radius: 16px;
  background: #fff;
}
.model-card h3 { margin: 0.65rem 0; color: var(--navy); font-size: 1.35rem; }
.model-card p { color: var(--muted); }
.model-metrics { display: grid; gap: 0.65rem; }
.model-metrics div { padding: 0.9rem; border-radius: 11px; background: #f8fafc; }
.model-metrics span { color: var(--muted); font-size: 0.68rem; font-weight: 800; text-transform: uppercase; }
.model-metrics strong { display: block; color: var(--navy); }
.model-metrics p { margin: 0.2rem 0 0; font-size: 0.8rem; }
.model-practice { margin: 1rem 0; padding: 1.25rem; border: 1px solid #bfdbfe; border-radius: 14px; background: var(--blue-soft); }
.model-practice input { margin: 0.8rem 0; }
.model-live { display: flex; align-items: baseline; justify-content: space-between; gap: 1rem; }
.model-live span { color: var(--muted); }
.model-live strong { color: var(--navy); font-size: 1.55rem; }
.mini-bars { display: grid; gap: 0.65rem; margin-top: 1rem; }
.mini-bars div { display: grid; grid-template-columns: 145px minmax(0, 1fr) 80px; gap: 0.6rem; align-items: center; font-size: 0.78rem; }
.mini-bars span { color: var(--muted); }
.mini-bars i { display: block; width: 10%; height: 10px; border-radius: 999px; background: var(--blue); transition: width 0.3s ease; }
.mini-bars strong { color: var(--navy); text-align: right; }
.model-question-box { margin-inline: 0; }

.test-shell { margin-top: 2rem; padding: 1.4rem; border: 1px solid #bfdbfe; border-radius: 18px; background: linear-gradient(135deg, var(--blue-soft), #fff); }
.test-topline { display: flex; justify-content: space-between; gap: 1rem; color: var(--muted); font-size: 0.78rem; font-weight: 750; }
.test-progress { height: 7px; margin: 0.6rem 0 1.3rem; overflow: hidden; border-radius: 999px; background: #dbeafe; }
.test-progress span { display: block; width: 0; height: 100%; background: var(--blue); transition: width 0.3s ease; }
#testQuestionArea h3 { margin: 0.65rem 0 1rem; color: var(--navy); font-size: 1.45rem; line-height: 1.35; }
.test-options { grid-template-columns: 1fr 1fr; }
.explanation { min-height: 3.3rem; font-weight: 650; }
.test-result { display: grid; grid-template-columns: auto minmax(0, 1fr); gap: 1.4rem; align-items: center; }
.result-ring {
  display: grid;
  width: 132px;
  aspect-ratio: 1;
  place-items: center;
  border-radius: 50%;
  background: conic-gradient(var(--blue) var(--score-angle, 0deg), #dbeafe 0);
  position: relative;
}
.result-ring::after { position: absolute; inset: 12px; border-radius: 50%; background: #fff; content: ""; }
.result-ring strong { position: relative; z-index: 1; color: var(--navy); font-size: 1.55rem; }
.test-result h3 { margin: 0; color: var(--navy); font-size: 1.6rem; }
.test-result p { color: var(--muted); }
.result-breakdown { display: flex; flex-wrap: wrap; gap: 0.5rem; margin-bottom: 1rem; }
.result-breakdown span { padding: 0.4rem 0.6rem; border-radius: 8px; background: #f8fafc; color: var(--navy); font-size: 0.75rem; font-weight: 750; }
.completion-card { margin-top: 1.2rem; padding: 1rem; border: 1px solid var(--line); border-radius: 13px; background: #fff; }
.completion-card > div:first-child { display: flex; justify-content: space-between; gap: 1rem; margin-bottom: 0.55rem; }
.completion-card span { color: var(--muted); }
.completion-card strong { color: var(--navy); }

footer { border-top: 1px solid var(--line); background: #fff; }
.footer-inner { min-height: 90px; display: flex; align-items: center; justify-content: space-between; gap: 1rem; color: var(--muted); font-size: 0.84rem; }
.footer-inner a { font-weight: 800; text-decoration: none; }

@media (max-width: 1080px) {
  .topbar { grid-template-columns: minmax(170px, 1fr) minmax(200px, 300px) auto; }
  .hero-grid { grid-template-columns: 1fr; }
  .hero-summary { max-width: 650px; }
  .lesson-layout { grid-template-columns: 1fr; }
  .lesson-nav { position: static; display: grid; grid-template-columns: repeat(4, 1fr); gap: 0.35rem; }
  .lesson-nav > strong { grid-column: 1 / -1; }
  .nav-score { grid-column: 1 / -1; }
  .graph-workspace { grid-template-columns: 230px minmax(0, 1fr); }
  .property-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .reading-layout { grid-template-columns: 1fr; }
  .reading-canvas-shell { height: 430px; }
}

@media (max-width: 820px) {
  .shell { width: min(100% - 1.5rem, 1220px); }
  .topbar { min-height: 4.5rem; grid-template-columns: 1fr auto; }
  .header-progress { grid-column: 1 / -1; padding-bottom: 0.75rem; }
  .hero { padding: 4.4rem 0 4rem; }
  .lesson-layout { padding-top: 1.4rem; }
  .lesson-nav { grid-template-columns: repeat(2, 1fr); }
  .lesson-section { padding: 2rem 1.15rem; }
  .lab { margin-inline: 0; }
  .concept-grid { grid-template-columns: 1fr; }
  .concept-arrow { transform: rotate(90deg); justify-self: center; }
  .machine-layout,
  .practice-box,
  .transform-layout,
  .model-card { grid-template-columns: 1fr; }
  .rule-grid { grid-template-columns: 1fr; }
  .graph-workspace { grid-template-columns: 1fr; }
  .graph-controls { border-right: 0; border-bottom: 1px solid var(--line); }
  .canvas-shell { height: 430px; }
  .transform-canvas-shell { height: 420px; }
  .practice-box .feedback { grid-column: auto; }
  .checkpoint { align-items: flex-start; flex-direction: column; }
  .checkpoint-button { width: 100%; }
  .test-options { grid-template-columns: 1fr; }
}

@media (max-width: 560px) {
  .site-header .outline-button.compact { min-height: 36px; padding: 0.45rem 0.6rem; }
  .brand span { display: none; }
  .hero h1 { font-size: clamp(2.45rem, 14vw, 4rem); }
  .hero-summary div { align-items: flex-start; flex-direction: column; gap: 0.15rem; }
  .lesson-nav { grid-template-columns: 1fr; }
  .choice-row,
  .answer-row,
  .preset-row { grid-template-columns: 1fr; }
  .property-grid { grid-template-columns: 1fr; }
  .canvas-shell,
  .transform-canvas-shell,
  .reading-canvas-shell { height: 360px; }
  .mini-bars div { grid-template-columns: 1fr; gap: 0.25rem; }
  .mini-bars strong { text-align: left; }
  .test-result { grid-template-columns: 1fr; }
  .result-ring { width: 115px; }
  .footer-inner { align-items: flex-start; flex-direction: column; justify-content: center; }
}