:root {
  color-scheme: light;
  --bg: #f6f7f9;
  --surface: #ffffff;
  --surface-strong: #eef3f6;
  --ink: #151923;
  --muted: #5f6b78;
  --line: #d8e1ea;
  --accent: #007f73;
  --accent-soft: #dff4ef;
  --coral: #d86f45;
  --blue: #376fb7;
  --gold: #b57b18;
  --family-surface: #16897d;
  --family-size: #456fb9;
  --family-charge: #c95f3a;
  --family-recognition: #9b741f;
  --shadow: 0 18px 50px rgba(17, 24, 39, 0.1);
  --radius: 8px;
  --max-width: 1220px;
  --plot-bg: #fbfcfd;
  --plot-grid: #e8edf2;
  --plot-text: #657180;
}

html[data-theme="dark"] {
  color-scheme: dark;
  --bg: #111419;
  --surface: #1a1f27;
  --surface-strong: #232a35;
  --ink: #f5f7fb;
  --muted: #b5bfcb;
  --line: #323b48;
  --accent: #45c7b5;
  --accent-soft: #143a36;
  --coral: #ff9b70;
  --blue: #8fb6ff;
  --gold: #f3c56b;
  --family-surface: #53c7b4;
  --family-size: #8fb6ff;
  --family-charge: #ff9b70;
  --family-recognition: #f3c56b;
  --shadow: 0 20px 60px rgba(0, 0, 0, 0.28);
  --plot-bg: #151a21;
  --plot-grid: #28313d;
  --plot-text: #aeb9c7;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-width: 320px;
  background:
    linear-gradient(90deg, rgba(0, 127, 115, 0.08), transparent 34%),
    linear-gradient(180deg, rgba(216, 111, 69, 0.07), transparent 38%),
    var(--bg);
  color: var(--ink);
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  line-height: 1.55;
}

a {
  color: inherit;
}

button,
input {
  font: inherit;
}

.app-header {
  position: sticky;
  top: 0;
  z-index: 10;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 1rem max(1rem, calc((100vw - var(--max-width)) / 2));
  border-bottom: 1px solid var(--line);
  background: color-mix(in srgb, var(--surface), transparent 8%);
  backdrop-filter: blur(16px);
}

.brand,
.app-header nav {
  display: flex;
  align-items: center;
  gap: 0.7rem;
}

.brand,
.app-header a {
  text-decoration: none;
}

.brand span {
  display: grid;
  width: 42px;
  height: 42px;
  place-items: center;
  border-radius: var(--radius);
  background: var(--ink);
  color: var(--surface);
  font-weight: 900;
}

.app-header nav a,
.theme-toggle,
.quiet-action,
.lesson-tabs button,
.instrument-card {
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--surface);
  color: var(--ink);
  cursor: pointer;
  font-weight: 850;
  min-height: 38px;
  padding: 0.55rem 0.75rem;
  text-decoration: none;
}

.app-shell {
  width: min(var(--max-width), calc(100% - 2rem));
  margin: 0 auto;
  padding: 4rem 0 5rem;
}

.hero,
.selector-section,
.lesson-shell,
.glossary-section,
.overview-card,
.part-detail,
.control-panel,
.response-panel,
.application-card,
.glossary-card {
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: color-mix(in srgb, var(--surface), transparent 2%);
  box-shadow: var(--shadow);
}

.hero {
  margin-bottom: 1rem;
  padding: 1.2rem;
}

.hero > div:first-child {
  max-width: 850px;
}

.eyebrow {
  margin: 0 0 0.7rem;
  color: var(--accent);
  font-size: 0.78rem;
  font-weight: 900;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

h1,
h2,
h3,
p {
  margin-top: 0;
}

h1 {
  margin-bottom: 0.8rem;
  font-size: clamp(2.35rem, 5.4vw, 4.6rem);
  line-height: 0.96;
}

h2 {
  margin-bottom: 0.6rem;
  font-size: 1.55rem;
  line-height: 1.12;
}

h3 {
  margin-bottom: 0.5rem;
  font-size: 1.05rem;
}

.hero p:last-child,
.section-heading p,
.instrument-card p,
.overview-card p,
.overview-card li,
.part-detail p,
.application-card p,
.glossary-card p,
.response-panel p {
  color: var(--muted);
}

.selector-section,
.lesson-shell,
.glossary-section {
  margin-top: 1rem;
  padding: 1rem;
}

.section-heading {
  max-width: 760px;
  margin-bottom: 1rem;
}

.instrument-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(210px, 1fr));
  gap: 0.85rem;
}

.instrument-card {
  position: relative;
  display: grid;
  min-height: 220px;
  gap: 0.75rem;
  overflow: hidden;
  padding: 1rem;
  text-align: left;
  transition: border-color 160ms ease, transform 160ms ease;
}

.instrument-card:hover,
.instrument-card.is-selected {
  border-color: var(--accent);
  transform: translateY(-3px);
}

.instrument-card::before {
  content: "";
  position: absolute;
  inset: 0;
  border-top: 4px solid var(--card-color, var(--accent));
  pointer-events: none;
}

.instrument-icon {
  display: grid;
  width: 58px;
  height: 58px;
  place-items: center;
  border: 1px solid color-mix(in srgb, var(--card-color, var(--accent)), var(--line) 45%);
  border-radius: var(--radius);
  background: color-mix(in srgb, var(--card-color, var(--accent)), transparent 88%);
  color: var(--card-color, var(--accent));
  font-size: 1.2rem;
  font-weight: 900;
}

.instrument-card strong,
.instrument-card small,
.instrument-card em {
  display: block;
}

.instrument-card small {
  color: var(--muted);
  font-weight: 700;
}

.instrument-card em {
  align-self: end;
  color: var(--accent);
  font-style: normal;
  font-weight: 900;
}

.lesson-shell[hidden] {
  display: none;
}

.selector-section[hidden] {
  display: none;
}

.lesson-header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 1rem;
  margin-bottom: 1rem;
}

.lesson-header p:last-child {
  margin-bottom: 0;
  max-width: 72ch;
  color: var(--muted);
}

.lesson-actions,
.lesson-tabs {
  display: flex;
  flex-wrap: wrap;
  gap: 0.55rem;
}

.lesson-tabs {
  margin-bottom: 1rem;
}

.lesson-tabs button.is-active {
  border-color: var(--accent);
  background: var(--accent);
  color: #ffffff;
}

.tab-panel {
  display: none;
}

.tab-panel.is-active {
  display: block;
}

.overview-grid,
.application-grid,
.glossary-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.85rem;
}

.family-intro {
  display: grid;
  grid-template-columns: minmax(260px, 0.85fr) minmax(320px, 1.15fr);
  gap: 1rem;
  align-items: end;
  margin-bottom: 1rem;
}

.family-intro h3,
.family-intro p {
  margin-bottom: 0;
}

.family-intro > p {
  color: var(--muted);
}

.hplc-family-map {
  display: grid;
  grid-template-areas:
    ". top ."
    "left hub right"
    ". bottom .";
  grid-template-columns: minmax(220px, 1fr) minmax(170px, 0.72fr) minmax(220px, 1fr);
  gap: 3.5rem 4.5rem;
  align-items: center;
  min-height: 520px;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background:
    linear-gradient(90deg, color-mix(in srgb, var(--line), transparent 76%) 1px, transparent 1px),
    linear-gradient(180deg, color-mix(in srgb, var(--line), transparent 80%) 1px, transparent 1px),
    var(--surface-strong);
  background-size: 34px 34px;
  padding: 2rem;
}

.family-group {
  position: relative;
  z-index: 1;
  display: grid;
  gap: 0.55rem;
}

.family-group--top {
  grid-area: top;
}

.family-group--left {
  grid-area: left;
}

.family-group--right {
  grid-area: right;
}

.family-group--bottom {
  grid-area: bottom;
}

.family-group::before,
.family-group::after {
  content: "";
  position: absolute;
  z-index: -1;
  background: color-mix(in srgb, var(--family-color), var(--line) 38%);
}

.family-group--top::after,
.family-group--bottom::before {
  left: 50%;
  width: 2px;
  height: 3.6rem;
  transform: translateX(-50%);
}

.family-group--top::after {
  top: calc(100% + 0.1rem);
}

.family-group--bottom::before {
  bottom: calc(100% + 0.1rem);
}

.family-group--left::after,
.family-group--right::before {
  top: 50%;
  width: 4.6rem;
  height: 2px;
  transform: translateY(-50%);
}

.family-group--left::after {
  left: calc(100% + 0.1rem);
}

.family-group--right::before {
  right: calc(100% + 0.1rem);
}

.family-group-label {
  color: var(--family-color);
  font-size: 0.72rem;
  font-weight: 900;
  letter-spacing: 0.08em;
  text-align: center;
  text-transform: uppercase;
}

.family-branch-list {
  display: grid;
  gap: 0.45rem;
}

.family-branch {
  display: grid;
  grid-template-columns: minmax(88px, auto) 1fr;
  gap: 0.65rem;
  align-items: center;
  min-height: 48px;
  border: 1px solid var(--line);
  border-left: 4px solid var(--family-color);
  border-radius: var(--radius);
  background: var(--surface);
  color: var(--ink);
  cursor: pointer;
  padding: 0.55rem 0.7rem;
  text-align: left;
  transition: border-color 160ms ease, background-color 160ms ease, transform 160ms ease;
}

.family-branch:hover,
.family-branch.is-active {
  border-color: var(--family-color);
  background: color-mix(in srgb, var(--family-color), transparent 90%);
  transform: translateY(-1px);
}

.family-branch strong {
  color: var(--family-color);
  font-size: 0.78rem;
}

.family-branch span {
  color: var(--muted);
  font-size: 0.82rem;
  font-weight: 750;
}

.family-hub {
  grid-area: hub;
  z-index: 2;
  display: grid;
  min-height: 160px;
  place-content: center;
  border: 2px solid var(--accent);
  border-radius: var(--radius);
  background: var(--surface);
  box-shadow: 0 14px 30px color-mix(in srgb, var(--accent), transparent 84%);
  padding: 1rem;
  text-align: center;
}

.family-hub span {
  color: var(--coral);
  font-size: 0.72rem;
  font-weight: 900;
  letter-spacing: 0.12em;
}

.family-hub strong {
  font-size: 1.6rem;
}

.family-hub small {
  color: var(--muted);
  font-weight: 700;
  line-height: 1.35;
}

.hplc-branch-detail {
  margin-top: 1rem;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--surface);
  padding: 1rem;
}

.family-format-note {
  margin: 0.75rem 0 0;
  color: var(--muted);
  font-size: 0.9rem;
}

.family-format-note strong {
  color: var(--ink);
}

.branch-detail-heading {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 1rem;
}

.branch-detail-heading h3,
.branch-detail-heading .eyebrow {
  margin-bottom: 0.25rem;
}

.branch-detail-heading > span {
  border: 1px solid var(--line);
  border-radius: var(--radius);
  color: var(--accent);
  font-size: 0.78rem;
  font-weight: 900;
  padding: 0.4rem 0.55rem;
}

.branch-summary {
  max-width: 92ch;
  color: var(--muted);
}

.branch-facts {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0;
  margin: 0;
  border-top: 1px solid var(--line);
}

.branch-facts > div {
  padding: 0.8rem 0.9rem 0 0;
}

.branch-facts dt {
  color: var(--accent);
  font-size: 0.72rem;
  font-weight: 900;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.branch-facts dd {
  margin: 0.25rem 0 0;
  color: var(--muted);
}

.column-guide {
  margin-top: 1rem;
  border-top: 1px solid var(--line);
}

.column-guide summary {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto auto;
  gap: 0.75rem;
  align-items: center;
  cursor: pointer;
  list-style: none;
  padding: 0.9rem 0 0;
}

.column-guide summary::-webkit-details-marker {
  display: none;
}

.column-guide summary > span:first-child {
  display: grid;
}

.column-guide summary small {
  color: var(--accent);
  font-size: 0.7rem;
  font-weight: 900;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.column-guide summary strong {
  color: var(--ink);
}

.column-guide-count {
  color: var(--muted);
  font-size: 0.8rem;
  font-weight: 800;
}

.column-guide-toggle {
  display: grid;
  width: 2rem;
  height: 2rem;
  place-items: center;
  border: 1px solid var(--line);
  color: var(--accent);
  font-size: 1.15rem;
  font-weight: 900;
}

.column-guide[open] .column-guide-toggle {
  font-size: 0;
}

.column-guide[open] .column-guide-toggle::before {
  content: "-";
  font-size: 1.15rem;
}

.column-option-list {
  margin-top: 0.85rem;
  border-top: 1px solid var(--line);
}

.column-option-row {
  display: grid;
  grid-template-columns: minmax(150px, 0.65fr) minmax(220px, 1fr) minmax(220px, 1fr);
  gap: 1rem;
  padding: 0.85rem 0;
  border-bottom: 1px solid var(--line);
}

.column-option-name {
  display: grid;
  align-content: start;
}

.column-option-name strong {
  color: var(--accent);
}

.column-option-name small {
  margin-top: 0.2rem;
  color: var(--muted);
  line-height: 1.35;
}

.column-option-row p {
  margin: 0;
  color: var(--muted);
}

.column-option-row p > span {
  display: block;
  margin-bottom: 0.2rem;
  color: var(--ink);
  font-size: 0.7rem;
  font-weight: 900;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.column-guide-note {
  margin: 0.75rem 0 0;
  color: var(--muted);
  font-size: 0.82rem;
}

.overview-card,
.application-card,
.glossary-card {
  padding: 1rem;
  box-shadow: none;
}

.overview-card ul {
  margin: 0;
  padding-left: 1.1rem;
}

.overview-card li {
  margin-bottom: 0.4rem;
}

.overview-card li::marker {
  color: var(--coral);
}

.diagram-layout,
.control-layout {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(260px, 340px);
  gap: 1rem;
  align-items: stretch;
}

.control-layout {
  grid-template-columns: minmax(260px, 340px) minmax(0, 1fr);
}

.instrument-diagram {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(135px, 1fr));
  gap: 0.75rem;
  min-height: 290px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background:
    linear-gradient(90deg, color-mix(in srgb, var(--line), transparent 72%) 1px, transparent 1px),
    linear-gradient(180deg, color-mix(in srgb, var(--line), transparent 78%) 1px, transparent 1px),
    var(--surface-strong);
  background-size: 34px 34px;
  padding: 1rem;
}

.diagram-node {
  position: relative;
  display: grid;
  align-content: center;
  min-height: 118px;
  border: 1px solid color-mix(in srgb, var(--accent), var(--line) 48%);
  border-radius: var(--radius);
  background: color-mix(in srgb, var(--surface), transparent 3%);
  color: var(--ink);
  cursor: pointer;
  gap: 0.35rem;
  padding: 0.85rem;
  text-align: left;
  transition: border-color 160ms ease, transform 160ms ease;
}

.diagram-node:hover,
.diagram-node.is-active {
  border-color: var(--accent);
  transform: translateY(-2px);
}

.diagram-node::after {
  content: ">";
  position: absolute;
  right: -0.55rem;
  top: 50%;
  color: var(--coral);
  font-weight: 900;
  transform: translateY(-50%);
}

.diagram-node:last-child::after {
  content: "";
}

.diagram-node span {
  display: grid;
  width: 34px;
  height: 34px;
  place-items: center;
  border-radius: 999px;
  background: var(--accent-soft);
  color: var(--accent);
  font-size: 0.8rem;
  font-weight: 900;
}

.diagram-node strong {
  line-height: 1.15;
}

.diagram-node small {
  color: var(--muted);
  font-weight: 700;
  line-height: 1.3;
}

.part-detail {
  align-self: stretch;
  padding: 1rem;
}

.part-detail span {
  display: inline-flex;
  margin-bottom: 0.85rem;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  color: var(--coral);
  font-weight: 900;
  padding: 0.38rem 0.5rem;
}

.control-panel,
.response-panel {
  padding: 1rem;
}

.control-list {
  display: grid;
  gap: 0.9rem;
}

.mode-field {
  display: grid;
  gap: 0.55rem;
}

.mode-field > span {
  color: var(--muted);
  font-size: 0.78rem;
  font-weight: 900;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.mode-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.5rem;
}

.mode-grid button {
  min-height: 82px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--surface);
  color: var(--ink);
  cursor: pointer;
  padding: 0.65rem;
  text-align: left;
  transition: background-color 160ms ease, border-color 160ms ease, transform 160ms ease;
}

.mode-grid button:hover,
.mode-grid button.is-active {
  border-color: var(--accent);
  background: var(--accent-soft);
}

.mode-grid button:hover {
  transform: translateY(-2px);
}

.mode-grid strong,
.mode-grid small {
  display: block;
}

.mode-grid small {
  margin-top: 0.25rem;
  color: var(--muted);
  font-size: 0.76rem;
  font-weight: 700;
  line-height: 1.35;
}

.slider-field {
  display: grid;
  gap: 0.45rem;
}

.slider-field label {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  color: var(--muted);
  font-size: 0.78rem;
  font-weight: 900;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.slider-field strong {
  color: var(--accent);
}

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

.response-panel {
  display: grid;
  gap: 0.85rem;
}

.response-panel canvas {
  display: block;
  width: 100%;
  height: 260px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--plot-bg);
}

.metric-row {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.55rem;
}

.metric-card {
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--surface-strong);
  padding: 0.65rem;
}

.metric-card span {
  display: block;
  color: var(--muted);
  font-size: 0.72rem;
  font-weight: 900;
  text-transform: uppercase;
}

.metric-card strong {
  display: block;
  margin-top: 0.2rem;
  color: var(--coral);
  font-size: 1.08rem;
}

.application-card {
  min-height: 145px;
}

.application-card span {
  display: inline-flex;
  margin-bottom: 0.75rem;
  border: 1px solid color-mix(in srgb, var(--accent), var(--line) 48%);
  border-radius: 999px;
  background: color-mix(in srgb, var(--accent), transparent 90%);
  color: var(--accent);
  font-size: 0.72rem;
  font-weight: 900;
  padding: 0.28rem 0.48rem;
}

.glossary-section {
  margin-top: 1rem;
}

.glossary-summary {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  cursor: pointer;
  list-style: none;
}

.glossary-summary::-webkit-details-marker {
  display: none;
}

.glossary-summary .section-heading {
  margin-bottom: 0;
}

.glossary-summary > span {
  display: grid;
  width: 2rem;
  height: 2rem;
  place-items: center;
  border: 1px solid var(--line);
  color: var(--accent);
  font-size: 1.2rem;
  font-weight: 900;
}

.glossary-section[open] .glossary-summary {
  margin-bottom: 1rem;
}

.glossary-section[open] .glossary-summary > span {
  transform: rotate(45deg);
}

.glossary-card h3 {
  color: var(--accent);
}

@media (max-width: 980px) {
  .hero,
  .diagram-layout,
  .control-layout,
  .overview-grid,
  .application-grid,
  .glossary-grid {
    grid-template-columns: 1fr;
  }

  .lesson-header {
    display: grid;
  }

  .family-intro {
    grid-template-columns: 1fr;
    align-items: start;
  }

  .hplc-family-map {
    grid-template-areas:
      "hub"
      "top"
      "right"
      "left"
      "bottom";
    grid-template-columns: minmax(0, 1fr);
    gap: 1.25rem;
    min-height: 0;
    padding: 1rem;
  }

  .family-group::before,
  .family-group::after {
    display: none;
  }

  .family-hub {
    min-height: 120px;
  }

  .column-option-row {
    grid-template-columns: minmax(140px, 0.55fr) minmax(0, 1fr);
  }

  .column-option-row p:last-child {
    grid-column: 2;
  }

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

@media (max-width: 640px) {
  .app-shell {
    padding-top: 2.5rem;
  }

  .lesson-actions,
  .lesson-actions > * {
    width: 100%;
  }

  .lesson-tabs {
    flex-wrap: nowrap;
    overflow-x: auto;
    padding-bottom: 0.35rem;
    scrollbar-width: none;
  }

  .lesson-tabs::-webkit-scrollbar {
    display: none;
  }

  .lesson-tabs button {
    flex: 0 0 auto;
    width: auto;
  }

  .instrument-grid,
  .metric-row,
  .mode-grid,
  .branch-facts {
    grid-template-columns: 1fr;
  }

  .branch-detail-heading {
    display: grid;
  }

  .branch-detail-heading > span {
    justify-self: start;
  }

  .column-guide summary {
    grid-template-columns: minmax(0, 1fr) auto;
  }

  .column-guide-count {
    display: none;
  }

  .column-option-row {
    grid-template-columns: 1fr;
    gap: 0.65rem;
  }

  .column-option-row p:last-child {
    grid-column: auto;
  }

  .instrument-diagram {
    grid-template-columns: 1fr;
  }

  .diagram-node::after {
    bottom: -0.85rem;
    left: 50%;
    right: auto;
    top: auto;
    transform: translateX(-50%) rotate(90deg);
  }
}