:root {
  color-scheme: light;
  --ink: #18202f;
  --muted: #596579;
  --line: #d9e0ea;
  --paper: #f7f8fb;
  --panel: #ffffff;
  --teal: #087f8c;
  --red: #c43e4f;
  --amber: #b97912;
  --green: #287d4f;
  --shadow: 0 18px 50px rgba(28, 37, 54, 0.12);
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  color: var(--ink);
  background: var(--paper);
  font-family:
    Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI",
    sans-serif;
}

.topbar {
  position: sticky;
  top: 0;
  z-index: 10;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
  min-height: 68px;
  padding: 12px clamp(18px, 5vw, 72px);
  border-bottom: 1px solid rgba(24, 32, 47, 0.1);
  background: rgba(247, 248, 251, 0.92);
  backdrop-filter: blur(16px);
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  color: var(--ink);
  font-weight: 800;
  text-decoration: none;
  white-space: nowrap;
}

.brand-mark {
  display: grid;
  width: 34px;
  height: 34px;
  place-items: center;
  border-radius: 8px;
  background: var(--ink);
  color: #fff;
}

.nav {
  display: flex;
  flex-wrap: wrap;
  justify-content: flex-end;
  gap: 8px;
}

.nav a {
  min-height: 36px;
  padding: 8px 12px;
  border-radius: 8px;
  color: var(--muted);
  font-size: 0.94rem;
  font-weight: 650;
  text-decoration: none;
}

.nav a:hover {
  background: #e9edf3;
  color: var(--ink);
}

.nav a.active {
  background: var(--ink);
  color: #fff;
}

.hero,
.band,
.page-intro {
  padding: clamp(28px, 5vw, 72px) clamp(18px, 5vw, 72px);
}

.hero {
  min-height: calc(100vh - 68px);
  display: grid;
  align-content: start;
  gap: 28px;
}

.home-hero {
  grid-template-columns: minmax(0, 0.9fr) minmax(320px, 1.1fr);
  align-items: center;
}

.hero-copy,
.section-heading {
  max-width: 760px;
}

.eyebrow {
  margin: 0 0 8px;
  color: var(--teal);
  font-size: 0.78rem;
  font-weight: 800;
  letter-spacing: 0;
  text-transform: uppercase;
}

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

h1 {
  max-width: 820px;
  margin-bottom: 14px;
  font-size: clamp(2.35rem, 7vw, 5.9rem);
  line-height: 0.95;
  letter-spacing: 0;
}

h2 {
  margin-bottom: 10px;
  font-size: clamp(1.75rem, 3vw, 3rem);
  line-height: 1.05;
  letter-spacing: 0;
}

h3 {
  margin-bottom: 10px;
  font-size: 1.05rem;
}

.hero-copy p:not(.eyebrow),
.section-heading p:not(.eyebrow),
.page-intro p:not(.eyebrow) {
  color: var(--muted);
  font-size: clamp(1rem, 2vw, 1.24rem);
  line-height: 1.55;
}

.page-intro {
  padding-bottom: 28px;
}

.page-intro h1 {
  margin-bottom: 12px;
}

.action-row {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin-top: 24px;
}

.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 44px;
  padding: 10px 16px;
  border: 1px solid var(--line);
  border-radius: 8px;
  color: var(--ink);
  background: #fff;
  font-weight: 800;
  text-decoration: none;
}

.button.primary {
  border-color: var(--teal);
  background: var(--teal);
  color: #fff;
}

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

.feature-card {
  min-height: 220px;
  padding: 20px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--panel);
  color: var(--ink);
  text-decoration: none;
  box-shadow: var(--shadow);
}

.feature-card span {
  color: var(--teal);
  font-weight: 900;
}

.feature-card h2 {
  margin-top: 34px;
  font-size: 1.4rem;
}

.feature-card p {
  color: var(--muted);
  line-height: 1.5;
}

.unit-layout,
.lab-layout {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(280px, 360px);
  gap: 18px;
  align-items: stretch;
}

.simulation-panel,
.control-panel,
.topic-card,
.subject-card,
.explain-block {
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--panel);
  box-shadow: var(--shadow);
}

.simulation-panel {
  overflow: hidden;
}

canvas {
  display: block;
  width: 100%;
  height: auto;
  background: #ffffff;
}

.control-panel {
  display: flex;
  flex-direction: column;
  gap: 18px;
  padding: 20px;
}

.sine-tool {
  display: grid;
  gap: 18px;
  max-width: 1040px;
}

.sine-controls {
  display: grid;
  gap: 12px;
  max-width: 760px;
}

.btn-row {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  align-items: center;
}

.tool-button {
  min-height: 36px;
  border: 1px solid #9aa5b5;
  border-radius: 8px;
  padding: 7px 14px;
  background: transparent;
  color: inherit;
  cursor: pointer;
  font: inherit;
  font-size: 0.9rem;
  font-weight: 750;
}

.tool-button:hover {
  background: #e9edf3;
}

.ctrl {
  display: grid;
  grid-template-columns: 78px minmax(160px, 1fr) 72px;
  gap: 10px;
  align-items: center;
  color: var(--muted);
  font-size: 0.9rem;
  font-weight: 750;
}

.ctrl strong {
  color: var(--ink);
  font-variant-numeric: tabular-nums;
}

.stats {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 10px;
}

.stat {
  min-height: 82px;
  border-radius: 8px;
  background: rgba(24, 32, 47, 0.055);
  padding: 14px;
  text-align: center;
}

.stat-label {
  margin-bottom: 5px;
  color: var(--muted);
  font-size: 0.82rem;
  font-weight: 750;
}

.stat-value {
  font-size: 1.2rem;
  font-weight: 850;
  font-variant-numeric: tabular-nums;
}

.angle-readout {
  display: grid;
  gap: 4px;
  padding-bottom: 16px;
  border-bottom: 1px solid var(--line);
}

.angle-readout span,
.angle-readout small,
.slider-label,
.select-label,
.inline-controls label {
  color: var(--muted);
  font-size: 0.9rem;
  font-weight: 700;
}

.angle-readout strong {
  font-size: 2.4rem;
  line-height: 1;
}

.slider-label,
.select-label {
  display: grid;
  gap: 8px;
}

input,
select {
  accent-color: var(--teal);
}

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

select {
  min-height: 42px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fff;
  color: var(--ink);
  font: inherit;
}

.toggle-row {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
}

.toggle-row label {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  min-height: 36px;
  padding: 8px 10px;
  border: 1px solid var(--line);
  border-radius: 8px;
  font-weight: 700;
}

.values {
  display: grid;
  gap: 10px;
  margin: 0;
}

.values div {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 16px;
  min-height: 44px;
  padding: 10px 0;
  border-top: 1px solid var(--line);
}

.values dt {
  color: var(--muted);
  font-weight: 700;
}

.values dd {
  margin: 0;
  font-family: ui-monospace, SFMono-Regular, Consolas, "Liberation Mono", monospace;
  font-size: 1.15rem;
  font-weight: 800;
}

.band {
  border-top: 1px solid rgba(24, 32, 47, 0.09);
}

.section-heading {
  margin-bottom: 22px;
}

.formula {
  margin: 0;
  padding: 14px;
  border-left: 4px solid var(--teal);
  background: #eef8f9;
  color: var(--ink);
  font-family: ui-monospace, SFMono-Regular, Consolas, "Liberation Mono", monospace;
  line-height: 1.45;
}

.inline-controls {
  display: grid;
  grid-template-columns: auto minmax(160px, 1fr) minmax(130px, auto);
  gap: 14px;
  align-items: center;
  padding: 14px 18px 18px;
  border-top: 1px solid var(--line);
}

.inline-controls strong {
  justify-self: end;
}

.topic-grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 16px;
}

.topic-card {
  min-height: 180px;
  padding: 20px;
}

.topic-card p {
  color: var(--muted);
  line-height: 1.55;
}

.subject-grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 16px;
}

.subject-card {
  display: block;
  min-height: 250px;
  padding: 20px;
  color: var(--ink);
  text-decoration: none;
}

.subject-card h2 {
  font-size: 1.35rem;
}

.subject-card p {
  color: var(--muted);
  line-height: 1.55;
}

.subject-card a {
  display: inline-flex;
  margin-top: 10px;
  color: var(--teal);
  font-weight: 800;
  text-decoration: none;
}

.explain-list {
  display: grid;
  gap: 18px;
  padding: 0 clamp(18px, 5vw, 72px) clamp(28px, 5vw, 72px);
}

.explain-block {
  padding: 24px;
}

.explain-block h2 {
  font-size: clamp(1.35rem, 2vw, 2rem);
}

.explain-block p {
  max-width: 860px;
  color: var(--muted);
  line-height: 1.65;
}

.explain-points {
  display: grid;
  gap: 10px;
  max-width: 900px;
  margin: 0;
  padding-left: 20px;
  color: var(--muted);
  line-height: 1.6;
}

.variable-list {
  display: grid;
  grid-template-columns: minmax(72px, 140px) minmax(0, 1fr);
  gap: 10px 16px;
  max-width: 900px;
  margin: 18px 0 0;
  color: var(--muted);
  line-height: 1.55;
}

.variable-list dt {
  color: var(--ink);
  font-family: ui-monospace, SFMono-Regular, Consolas, "Liberation Mono", monospace;
  font-weight: 900;
}

.variable-list dd {
  margin: 0;
}

.mini-sim-panel {
  display: grid;
  grid-template-columns: minmax(260px, 420px) minmax(260px, 1fr);
  gap: 16px;
  max-width: 980px;
}

.mini-controls,
.mini-output,
.mini-visual-wrap {
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--panel);
  box-shadow: var(--shadow);
}

.mini-controls {
  display: grid;
  gap: 14px;
  padding: 18px;
}

.mini-control {
  display: grid;
  grid-template-columns: minmax(95px, 140px) minmax(140px, 1fr) 64px;
  gap: 10px;
  align-items: center;
  color: var(--muted);
  font-size: 0.9rem;
  font-weight: 750;
}

.mini-control strong {
  color: var(--ink);
  font-variant-numeric: tabular-nums;
  text-align: right;
}

.mini-visual-wrap {
  overflow: hidden;
}

.mini-visual {
  display: block;
  width: 100%;
  min-height: 240px;
  border: 0;
  border-bottom: 1px solid var(--line);
  border-radius: 0;
  box-shadow: none;
}

.mini-output {
  min-height: 120px;
  display: grid;
  align-content: center;
  padding: 22px;
  border: 0;
  border-left: 5px solid var(--teal);
  border-radius: 0;
  box-shadow: none;
  color: var(--ink);
  font-family: ui-monospace, SFMono-Regular, Consolas, "Liberation Mono", monospace;
  font-size: clamp(1rem, 2vw, 1.25rem);
  line-height: 1.7;
}

.symbol-line {
  margin-bottom: 8px;
  color: var(--teal);
  font-size: 1.15em;
  font-weight: 850;
}

.solid-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 18px;
}

.solid-card {
  display: grid;
  gap: 14px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--panel);
  padding: 18px;
  box-shadow: var(--shadow);
}

.solid-card canvas {
  width: 100%;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fff;
}

.solid-card h3 {
  margin-bottom: 6px;
  font-size: 1.35rem;
}

.solid-card p:not(.formula) {
  margin-bottom: 0;
  color: var(--muted);
  line-height: 1.5;
}

.solid-result {
  min-height: 76px;
}

@media (max-width: 920px) {
  .topbar {
    align-items: flex-start;
    flex-direction: column;
  }

  .nav {
    justify-content: flex-start;
  }

  .unit-layout,
  .lab-layout,
  .topic-grid,
  .subject-grid,
  .home-hero {
    grid-template-columns: 1fr;
  }

  .mini-sim-panel {
    grid-template-columns: 1fr;
  }

  .solid-grid {
    grid-template-columns: 1fr;
  }

  .hero {
    min-height: auto;
  }
}

@media (max-width: 560px) {
  .topbar,
  .hero,
  .band,
  .page-intro,
  .explain-list {
    padding-left: 14px;
    padding-right: 14px;
  }

  .brand {
    white-space: normal;
  }

  .nav a {
    padding-left: 9px;
    padding-right: 9px;
  }

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

  .inline-controls strong {
    justify-self: start;
  }

  .quick-grid {
    grid-template-columns: 1fr;
  }

  .ctrl,
  .stats,
  .mini-control {
    grid-template-columns: 1fr;
  }

  .mini-control strong {
    text-align: left;
  }
}