:root {
  color-scheme: light;
  --ink: #20242c;
  --muted: #596273;
  --line: #d7dee9;
  --paper: #fbfcfe;
  --panel: #ffffff;
  --blue: #2563a9;
  --teal: #0f766e;
  --green: #2f7d47;
  --red: #b43a3a;
  --amber: #b66f00;
  --violet: #6858c7;
  --rose: #a43d68;
  --soft-blue: #eef5fc;
  --soft-teal: #eef8f6;
  --soft-green: #eef8f1;
  --soft-red: #fff2f2;
  --soft-amber: #fff7e8;
  --soft-violet: #f3f1ff;
  --shadow: 0 14px 34px rgba(34, 43, 63, 0.09);
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  line-height: 1.55;
}

a {
  color: var(--blue);
}

.shell {
  display: grid;
  grid-template-columns: minmax(230px, 292px) minmax(0, 1fr);
  min-height: 100vh;
}

.sidebar {
  position: sticky;
  top: 0;
  height: 100vh;
  padding: 24px 20px;
  border-right: 1px solid var(--line);
  background: #f2f6fb;
  overflow-y: auto;
}

.course,
.eyebrow {
  color: var(--muted);
  font-size: 0.78rem;
  font-weight: 800;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.nav-title {
  margin: 8px 0 18px;
  font-size: 1.34rem;
  line-height: 1.15;
  letter-spacing: 0;
}

nav {
  display: grid;
  gap: 3px;
}

nav a {
  display: block;
  padding: 8px 10px;
  border: 1px solid transparent;
  border-radius: 8px;
  color: #283142;
  font-size: 0.94rem;
  text-decoration: none;
}

nav a:hover,
nav a:focus,
nav a.active {
  border-color: #bdc9da;
  background: #ffffff;
  outline: none;
}

.aside-note {
  margin-top: 16px;
  padding-top: 16px;
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-size: 0.9rem;
}

main {
  min-width: 0;
}

section {
  padding: 58px clamp(22px, 5vw, 76px);
  border-bottom: 1px solid var(--line);
}

section:nth-child(even) {
  background: #ffffff;
}

.hero {
  display: grid;
  grid-template-columns: minmax(0, 1.05fr) minmax(320px, 0.95fr);
  gap: clamp(28px, 5vw, 58px);
  align-items: center;
  min-height: 78vh;
  background: linear-gradient(180deg, #f8fbff 0%, #ffffff 100%);
}

h2 {
  margin: 0 0 14px;
  font-size: clamp(1.65rem, 3.2vw, 4.2rem);
  line-height: 1.02;
  letter-spacing: 0;
}

section:not(.hero) h2 {
  font-size: clamp(1.55rem, 2.6vw, 2.55rem);
  line-height: 1.08;
}

h3 {
  margin: 0 0 8px;
  font-size: 1.08rem;
  line-height: 1.18;
  letter-spacing: 0;
}

p {
  max-width: 80ch;
}

.lead {
  color: #394557;
  font-size: clamp(1.05rem, 1.45vw, 1.32rem);
  max-width: 68ch;
}

.hero-actions,
.resource-links {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin-top: 22px;
}

.primary-link,
.secondary-link,
.resource-links a {
  display: inline-flex;
  align-items: center;
  min-height: 40px;
  border-radius: 8px;
  padding: 9px 13px;
  font-weight: 800;
  text-decoration: none;
}

.primary-link {
  background: var(--ink);
  color: #ffffff;
}

.secondary-link,
.resource-links a {
  border: 1px solid var(--line);
  background: #ffffff;
  color: #283142;
}

.section-head {
  max-width: 980px;
  margin-bottom: 28px;
}

.grid-2 {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(310px, 0.95fr);
  gap: clamp(26px, 4vw, 54px);
  align-items: start;
}

.viz-panel,
.concept,
.comparison article,
.practice-grid article {
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--panel);
  box-shadow: var(--shadow);
}

.viz-panel {
  padding: clamp(18px, 2.6vw, 26px);
}

.hero-viz {
  box-shadow: none;
}

.concept,
.comparison article,
.practice-grid article {
  padding: 20px;
}

.score-note {
  margin-top: 18px;
  border: 1px solid #cbd6e6;
  border-radius: 8px;
  padding: 18px 20px;
  background: #f8fbff;
}

.score-note p {
  margin: 0 0 12px;
  color: var(--muted);
}

.score-formulas {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.score-formulas span {
  border: 1px solid #c8d4e4;
  border-radius: 8px;
  padding: 8px 10px;
  background: #ffffff;
  color: #334155;
  font-size: 0.88rem;
  font-weight: 800;
}

.panel-note {
  margin: 0 0 16px;
  color: var(--muted);
  font-size: 0.94rem;
}

canvas {
  display: block;
  width: 100%;
  max-width: 100%;
  height: auto;
  border: 1px solid #cbd6e6;
  border-radius: 8px;
  background: #f8fbff;
}

.timeline {
  display: grid;
  grid-template-columns: repeat(5, minmax(140px, 1fr));
  gap: 12px;
  margin: 26px 0 32px;
}

.step {
  min-height: 132px;
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 16px;
  background: #ffffff;
}

.step strong {
  display: block;
  margin-bottom: 8px;
  font-size: 1.02rem;
}

.step span {
  color: var(--muted);
  font-size: 0.94rem;
}

.formula {
  display: inline-block;
  margin: 14px 0;
  border: 1px solid #c7d4e4;
  border-radius: 8px;
  padding: 10px 12px;
  background: var(--soft-blue);
  color: #26364a;
  font-weight: 850;
}

.math-details {
  margin-top: 16px;
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 12px 14px;
  background: #ffffff;
}

.math-details summary {
  cursor: pointer;
  font-weight: 850;
}

.math-details p {
  margin-bottom: 0;
  color: var(--muted);
}

.controls {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin-bottom: 14px;
}

label {
  display: grid;
  gap: 6px;
  color: #334155;
  font-size: 0.86rem;
  font-weight: 850;
}

select,
input[type="range"] {
  width: 100%;
}

select {
  min-height: 40px;
  border: 1px solid #b8c5d7;
  border-radius: 8px;
  padding: 7px 36px 7px 10px;
  background: #ffffff;
  color: var(--ink);
  font: inherit;
  font-weight: 800;
}

.slider-stack {
  display: grid;
  gap: 10px;
  margin: 14px 0 16px;
}

.slider-row {
  display: grid;
  grid-template-columns: minmax(112px, 0.8fr) minmax(120px, 1fr) 44px;
  gap: 10px;
  align-items: center;
  color: #334155;
  font-size: 0.9rem;
  font-weight: 780;
}

.slider-value {
  justify-self: end;
  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  color: #475569;
}

.metric-strip {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 12px;
}

.metric-strip span {
  border: 1px solid #c8d4e4;
  border-radius: 8px;
  padding: 7px 10px;
  background: #f8fbff;
  color: #334155;
  font-size: 0.88rem;
  font-weight: 800;
}

.segmented {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin: 12px 0 16px;
}

.segmented button {
  border: 1px solid #bdc9da;
  border-radius: 8px;
  padding: 8px 10px;
  background: #ffffff;
  color: #334155;
  font: inherit;
  font-weight: 850;
  cursor: pointer;
}

.segmented button.active {
  border-color: var(--ink);
  background: var(--ink);
  color: #ffffff;
}

.concept-list {
  display: grid;
  gap: 12px;
}

.concept-list article {
  border-left: 5px solid var(--blue);
  padding: 12px 0 12px 16px;
}

.concept-list p {
  margin: 0;
  color: var(--muted);
}

.check-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 8px;
  margin: 12px 0 16px;
}

.check-grid.compact {
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.check-item {
  display: flex;
  align-items: flex-start;
  gap: 8px;
  border: 1px solid #d3dcea;
  border-radius: 8px;
  padding: 9px 10px;
  background: #ffffff;
  color: #334155;
  font-size: 0.89rem;
  font-weight: 760;
}

.check-item input {
  margin-top: 3px;
  accent-color: var(--blue);
}

.comparison {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 14px;
}

.comparison ul {
  margin: 10px 0 0;
  padding-left: 18px;
  color: var(--muted);
}

.practice-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 14px;
}

.practice-grid p {
  margin: 0;
  color: var(--muted);
}

.slide-preview {
  margin: 0;
}

.slide-viewer {
  display: grid;
  gap: 12px;
}

.slide-preview img {
  display: block;
  width: 100%;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #ffffff;
  box-shadow: var(--shadow);
}

.slide-preview figcaption {
  margin-top: 8px;
  color: var(--muted);
  font-size: 0.9rem;
}

.slide-controls {
  display: grid;
  grid-template-columns: minmax(96px, auto) minmax(96px, 1fr) minmax(96px, auto);
  gap: 8px;
  align-items: center;
}

.slide-controls button {
  min-height: 40px;
  border: 1px solid #bdc9da;
  border-radius: 8px;
  background: #ffffff;
  color: #283142;
  cursor: pointer;
  font: inherit;
  font-weight: 850;
}

.slide-controls button:hover,
.slide-controls button:focus {
  border-color: var(--ink);
  outline: none;
}

.slide-controls span {
  justify-self: center;
  color: #334155;
  font-weight: 850;
}

.reference-list {
  display: grid;
  gap: 8px;
  margin: 20px 0;
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 16px;
  background: #ffffff;
}

.reference-list p {
  margin: 0 0 4px;
  color: var(--muted);
}

.reference-list a {
  display: block;
  border: 1px solid #d3dcea;
  border-radius: 8px;
  padding: 8px 10px;
  background: #f8fbff;
  color: #283142;
  font-weight: 800;
  text-decoration: none;
}

.reference-list a:hover,
.reference-list a:focus {
  border-color: var(--blue);
  outline: none;
}

.glossary {
  display: grid;
  gap: 10px;
  margin-top: 22px;
}

.glossary div {
  display: grid;
  grid-template-columns: minmax(130px, 0.42fr) minmax(0, 1fr);
  gap: 12px;
  border-bottom: 1px solid var(--line);
  padding-bottom: 10px;
}

.glossary span {
  color: var(--muted);
}

@media (max-width: 1100px) {
  .hero,
  .grid-2 {
    grid-template-columns: 1fr;
  }

  .timeline {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .practice-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}

@media (max-width: 760px) {
  .shell {
    display: block;
  }

  .sidebar {
    position: static;
    height: auto;
    border-right: 0;
    border-bottom: 1px solid var(--line);
  }

  nav {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  section {
    padding: 42px 18px;
  }

  .timeline,
  .comparison,
  .practice-grid,
  .check-grid,
  .check-grid.compact {
    grid-template-columns: 1fr;
  }

  .slider-row {
    grid-template-columns: 1fr;
    gap: 4px;
  }

  .slider-value {
    justify-self: start;
  }

  .hero {
    min-height: auto;
  }

  .glossary div {
    grid-template-columns: 1fr;
    gap: 2px;
  }

  .slide-controls {
    grid-template-columns: 1fr;
  }

  .slide-controls span {
    justify-self: start;
  }
}