:root {
  --bg: #eceff1;
  --bg-soft: #f7f8f9;
  --panel: rgba(255, 255, 255, 0.88);
  --panel-strong: #ffffff;
  --panel-soft: #f4f5f6;
  --border: rgba(27, 31, 35, 0.1);
  --border-strong: rgba(27, 31, 35, 0.16);
  --text: #1c2228;
  --muted: #5c6670;
  --muted-soft: #7b8792;
  --accent: #31485d;
  --accent-strong: #203648;
  --accent-soft: rgba(49, 72, 93, 0.1);
  --shadow: 0 20px 48px rgba(27, 31, 35, 0.08);
  --radius-xl: 30px;
  --radius-lg: 22px;
  --radius-md: 18px;
  --radius-sm: 12px;
  --content-width: 1620px;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: "Instrument Sans", sans-serif;
  color: var(--text);
  background:
    radial-gradient(circle at top left, rgba(79, 97, 111, 0.12), transparent 34%),
    radial-gradient(circle at top right, rgba(43, 57, 68, 0.08), transparent 26%),
    linear-gradient(180deg, #f8f9fa 0%, #eceff1 100%);
}

button,
input,
select {
  font: inherit;
}

.page-shell {
  width: min(calc(100% - 44px), var(--content-width));
  margin: 22px auto 42px;
}

.card {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: var(--radius-xl);
  box-shadow: var(--shadow);
  backdrop-filter: blur(18px);
}

.hero {
  display: grid;
  grid-template-columns: minmax(0, 2.1fr) minmax(300px, 1fr);
  gap: 28px;
  padding: 34px;
  margin-bottom: 30px;
  position: relative;
  overflow: hidden;
}

.hero::after {
  content: "";
  position: absolute;
  inset: auto -10% -28% auto;
  width: 360px;
  height: 360px;
  border-radius: 50%;
  background: radial-gradient(circle, rgba(49, 72, 93, 0.18), rgba(49, 72, 93, 0));
  pointer-events: none;
}

.eyebrow,
.section-index {
  margin: 0 0 10px;
  font-size: 0.82rem;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--accent);
}

.hero h1 {
  margin: 0;
  font-size: clamp(2.5rem, 4vw, 4.6rem);
  line-height: 0.96;
  letter-spacing: -0.045em;
}

.hero-text {
  margin: 18px 0 24px;
  max-width: 760px;
  font-size: 1.07rem;
  line-height: 1.75;
  color: var(--muted);
}

.hero-objectives {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

.hero-objectives span {
  padding: 10px 14px;
  border-radius: 999px;
  background: var(--accent-soft);
  color: var(--accent-strong);
  font-size: 0.92rem;
  font-weight: 600;
}

.hero-side {
  display: flex;
  align-items: stretch;
}

.formula-card,
.math-card,
.summary-box,
.roadmap-box,
.chart-card,
.mini-card,
.matrix-card,
.insight-panel {
  background: rgba(245, 246, 247, 0.92);
  border: 1px solid rgba(27, 31, 35, 0.08);
  border-radius: var(--radius-lg);
}

.formula-card {
  width: 100%;
  padding: 24px;
}

.formula-label,
.matrix-label,
.chart-label,
.roadmap-title {
  margin: 0 0 10px;
  font-size: 0.84rem;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--muted-soft);
}

.formula {
  margin: 0;
  font-size: 1.52rem;
  color: var(--accent-strong);
}

.formula-note,
.section-lead,
.insight-panel,
.summary-box,
.project-notes,
.insight-list,
.control-note,
.matrix-display {
  color: var(--muted);
  line-height: 1.68;
}

.formula-note {
  margin: 12px 0 0;
}

.lab-layout {
  display: grid;
  grid-template-columns: 340px minmax(0, 1fr);
  gap: 30px;
  align-items: start;
}

.control-card {
  position: sticky;
  top: 18px;
  padding: 24px;
}

.section-header {
  display: flex;
  justify-content: space-between;
  gap: 24px;
  margin-bottom: 22px;
  align-items: flex-start;
}

.section-header.compact {
  margin-bottom: 18px;
}

.section-header h2 {
  margin: 0;
  font-size: 1.65rem;
  letter-spacing: -0.03em;
}

.section-lead {
  margin: 0;
  max-width: 470px;
  font-size: 0.98rem;
}

.lesson-column {
  display: grid;
  gap: 32px;
}

.lesson-card {
  padding: 30px;
}

.control-stack {
  display: grid;
  gap: 14px;
}

.control-group {
  display: grid;
  gap: 10px;
  padding: 16px;
  border-radius: var(--radius-md);
  background: rgba(245, 246, 247, 0.92);
  border: 1px solid rgba(27, 31, 35, 0.08);
}

.control-group span {
  font-weight: 600;
}

.control-group strong,
.control-group small {
  color: var(--muted);
}

.control-group input[type="range"] {
  width: 100%;
  accent-color: var(--accent);
}

.control-group select,
.retain-control input[type="number"],
.upload-group input[type="file"] {
  width: 100%;
  padding: 12px 14px;
  border-radius: 14px;
  border: 1px solid var(--border-strong);
  background: var(--panel-strong);
  color: var(--text);
}

.retain-control {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 84px;
  gap: 10px;
}

.upload-group input[type="file"] {
  border-style: dashed;
}

.button-row {
  display: grid;
  gap: 10px;
  margin-top: 18px;
}

.action-button {
  border: 1px solid var(--border);
  background: var(--panel-strong);
  color: var(--text);
  padding: 12px 16px;
  border-radius: 999px;
  cursor: pointer;
  transition: transform 180ms ease, box-shadow 180ms ease, background 180ms ease;
}

.action-button:hover {
  transform: translateY(-1px);
  box-shadow: 0 10px 20px rgba(27, 31, 35, 0.08);
}

.action-button.primary {
  background: var(--accent-strong);
  color: #f8fafb;
  border-color: var(--accent-strong);
}

.control-footer {
  display: grid;
  gap: 14px;
  margin-top: 18px;
}

.summary-box,
.roadmap-box,
.insight-panel,
.math-card,
.matrix-card {
  padding: 18px;
}

.roadmap-list {
  margin: 0;
  padding: 0;
  list-style: none;
  display: grid;
  gap: 10px;
}

.roadmap-list li {
  padding: 12px 14px;
  border-radius: 14px;
  background: rgba(255, 255, 255, 0.72);
  border: 1px solid rgba(27, 31, 35, 0.06);
  color: var(--muted);
  transition: transform 200ms ease, background 200ms ease, border-color 200ms ease, color 200ms ease;
}

.roadmap-list li.active {
  transform: translateX(6px);
  background: rgba(49, 72, 93, 0.12);
  border-color: rgba(49, 72, 93, 0.28);
  color: var(--accent-strong);
  font-weight: 600;
}

.section-grid {
  display: grid;
  grid-template-columns: minmax(0, 1.45fr) minmax(280px, 0.78fr);
  gap: 22px;
  align-items: stretch;
}

.info-column {
  display: grid;
  gap: 16px;
}

.concept-row,
.chart-grid,
.takeaway-grid,
.comparison-grid {
  display: grid;
  gap: 18px;
}

.concept-row {
  grid-template-columns: repeat(2, minmax(0, 1fr));
  margin-bottom: 20px;
}

.chart-grid {
  grid-template-columns: repeat(2, minmax(0, 1fr));
  margin-top: 18px;
}

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

.takeaway-grid {
  grid-template-columns: repeat(3, minmax(0, 1fr));
}

.chart-card,
.mini-card,
.plot-panel {
  padding: 18px;
}

.component-card-grid {
  display: grid;
  gap: 12px;
}

.component-card {
  padding: 15px 16px;
  border-radius: 16px;
  border: 1px solid rgba(27, 31, 35, 0.08);
  background: rgba(245, 246, 247, 0.94);
  cursor: pointer;
  transition: transform 180ms ease, border-color 180ms ease, box-shadow 180ms ease, background 180ms ease;
}

.component-card.retained {
  background: rgba(49, 72, 93, 0.1);
  border-color: rgba(49, 72, 93, 0.22);
}

.component-card.discarded {
  opacity: 0.72;
}

.component-card:hover {
  transform: translateY(-1px);
}

.component-card.selected {
  border-color: rgba(31, 95, 174, 0.45);
  box-shadow: inset 0 0 0 1px rgba(31, 95, 174, 0.18), 0 10px 24px rgba(27, 31, 35, 0.08);
  background: rgba(31, 95, 174, 0.12);
  opacity: 1;
}

.component-card.selected h3,
.component-card.selected strong {
  color: #1f5fae;
}

.component-card.selected p:last-child {
  color: #1f5fae;
  font-weight: 600;
}

.component-card h3,
.mini-card h3 {
  margin: 0 0 10px;
  font-size: 1.02rem;
}

.component-card p,
.mini-card p,
.summary-box p,
.insight-panel p,
.project-notes p {
  margin: 0 0 10px;
}

.topx-explanation {
  padding: 18px 20px;
  border-radius: var(--radius-lg);
  background: rgba(49, 72, 93, 0.08);
  border: 1px solid rgba(49, 72, 93, 0.12);
}

.plot-area {
  width: 100%;
  border-radius: var(--radius-lg);
  overflow: hidden;
  background: rgba(255, 255, 255, 0.5);
}

.tall-plot {
  min-height: 590px;
}

.wide-plot {
  min-height: 520px;
}

.medium-plot {
  min-height: 400px;
}

.matrix-display {
  display: grid;
  gap: 10px;
  margin-top: 12px;
  padding: 14px;
  border-radius: 16px;
  background: #fbfbfb;
  border: 1px solid rgba(27, 31, 35, 0.08);
  font-family: "IBM Plex Mono", monospace;
}

.matrix-row {
  display: grid;
  gap: 10px;
}

.matrix-cell {
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 46px;
  padding: 8px;
  border-radius: 12px;
  background: rgba(49, 72, 93, 0.05);
  color: var(--accent-strong);
}

.insight-list {
  margin: 0;
  padding-left: 18px;
}

.project-notes .code-tag {
  display: inline-flex;
  padding: 3px 8px;
  border-radius: 999px;
  background: rgba(27, 31, 35, 0.08);
  font-family: "IBM Plex Mono", monospace;
  font-size: 0.82rem;
  color: var(--text);
}

.help-badge {
  position: relative;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 18px;
  height: 18px;
  margin-left: 6px;
  border-radius: 50%;
  background: rgba(49, 72, 93, 0.12);
  color: var(--accent-strong);
  font-size: 0.75rem;
  font-weight: 700;
  cursor: help;
}

.help-badge::after {
  content: attr(data-tooltip);
  position: absolute;
  left: calc(100% + 10px);
  top: 50%;
  transform: translateY(-50%);
  width: 230px;
  padding: 10px 12px;
  border-radius: 12px;
  background: rgba(28, 34, 40, 0.94);
  color: #f6f8fa;
  font-size: 0.82rem;
  line-height: 1.45;
  opacity: 0;
  pointer-events: none;
  transition: opacity 160ms ease;
  z-index: 20;
}

.help-badge:hover::after {
  opacity: 1;
}

@media (max-width: 1380px) {
  .lab-layout {
    grid-template-columns: 1fr;
  }

  .control-card {
    position: static;
  }
}

@media (max-width: 1160px) {
  .hero,
  .section-grid,
  .concept-row,
  .chart-grid,
  .takeaway-grid,
  .comparison-grid {
    grid-template-columns: 1fr;
  }

  .section-header {
    flex-direction: column;
  }
}

@media (max-width: 760px) {
  .page-shell {
    width: min(calc(100% - 24px), var(--content-width));
    margin: 12px auto 24px;
  }

  .hero,
  .lesson-card,
  .control-card {
    padding: 20px;
    border-radius: 22px;
  }

  .retain-control {
    grid-template-columns: 1fr;
  }

  .help-badge::after {
    left: auto;
    right: 0;
    top: calc(100% + 10px);
    transform: none;
    width: 200px;
  }

  .tall-plot {
    min-height: 460px;
  }

  .wide-plot {
    min-height: 430px;
  }
}