:root {
  color-scheme: light;
  --ink: #16202a;
  --muted: #5a6875;
  --line: #d6dee6;
  --panel: #ffffff;
  --paper: #f7f9fb;
  --blue: #2364aa;
  --green: #2a8c6d;
  --red: #b84a3a;
  --yellow: #d39b25;
  --violet: #6e5bbf;
  --shadow: 0 18px 60px rgba(22, 32, 42, 0.1);
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  min-width: 320px;
  color: var(--ink);
  background: var(--paper);
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  line-height: 1.55;
}

.topbar {
  position: sticky;
  top: 0;
  z-index: 10;
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
  padding: 14px clamp(18px, 4vw, 48px);
  border-bottom: 1px solid var(--line);
  background: rgba(247, 249, 251, 0.92);
  backdrop-filter: blur(12px);
}

.topbar h1,
.topbar p {
  margin: 0;
}

.topbar h1 {
  font-size: clamp(1.1rem, 2vw, 1.5rem);
}

nav {
  display: flex;
  flex-wrap: wrap;
  justify-content: flex-end;
  gap: 8px;
  min-width: 0;
}

.chapter-switcher {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-left: 0;
}

.chapter-switch {
  min-height: 36px;
  padding: 7px 11px;
  border: 1px solid var(--line);
  background: #fff;
  cursor: pointer;
}

.chapter-switch.active {
  border-color: var(--blue);
  background: #edf5ff;
}

nav a,
button {
  color: var(--ink);
  font: inherit;
}

nav a {
  min-height: 36px;
  padding: 7px 11px;
  border: 1px solid transparent;
  text-decoration: none;
}

nav a:hover,
nav a:focus-visible {
  border-color: var(--line);
  background: #fff;
  outline: none;
}

main {
  overflow: hidden;
}

.chapter-view {
  display: none;
}

.chapter-view.active {
  display: block;
}

.hero {
  display: grid;
  grid-template-columns: minmax(0, 0.88fr) minmax(360px, 1.12fr);
  gap: clamp(22px, 5vw, 70px);
  align-items: center;
  min-height: calc(100vh - 72px);
  padding: clamp(28px, 5vw, 70px) clamp(18px, 5vw, 64px) 36px;
  background:
    linear-gradient(90deg, rgba(255, 255, 255, 0.7), rgba(255, 255, 255, 0.15)),
    radial-gradient(circle at 85% 20%, rgba(35, 100, 170, 0.11), transparent 34%),
    var(--paper);
}

.hero-copy {
  max-width: 700px;
  min-width: 0;
}

.kicker,
.eyebrow {
  color: var(--blue);
  font-size: 0.78rem;
  font-weight: 760;
  letter-spacing: 0;
  text-transform: uppercase;
}

.hero h2 {
  margin: 12px 0 18px;
  max-width: 760px;
  font-size: clamp(2.4rem, 5.9vw, 5.9rem);
  line-height: 0.98;
  letter-spacing: 0;
}

.hero p {
  max-width: 760px;
  color: var(--muted);
  font-size: clamp(1rem, 1.4vw, 1.16rem);
}

.robot-stage,
.mechanism-diagram,
.plot,
.detail-panel,
.pipeline,
.quiz-card,
.control-panel,
.visual-panel,
.formula-panel,
.joint-table-wrap,
.concept-card,
.task-card {
  border: 1px solid var(--line);
  background: var(--panel);
  box-shadow: var(--shadow);
}

.robot-stage {
  padding: clamp(16px, 3vw, 28px);
}

svg {
  display: block;
  width: 100%;
  height: auto;
}

.floor {
  fill: #d7e2eb;
}

.workspace-ring {
  fill: none;
  stroke: rgba(35, 100, 170, 0.25);
  stroke-width: 2;
}

.workspace-ring.inner {
  stroke-dasharray: 7 7;
}

.link {
  stroke: var(--blue);
  stroke-width: 18;
  stroke-linecap: round;
}

.link.secondary {
  stroke: var(--green);
}

.joint {
  fill: #fff;
  stroke: var(--ink);
  stroke-width: 4;
}

.end-effector {
  fill: var(--red);
}

.axis {
  stroke: var(--ink);
  stroke-width: 2;
  marker-end: url(#arrow);
}

.target circle {
  fill: rgba(184, 74, 58, 0.14);
  stroke: var(--red);
  stroke-width: 3;
}

.target path {
  stroke: var(--red);
  stroke-width: 2;
}

.joint-panel {
  display: grid;
  gap: 14px;
  margin-top: 16px;
}

label {
  display: grid;
  grid-template-columns: 94px 72px minmax(120px, 1fr);
  align-items: center;
  gap: 12px;
  color: var(--muted);
  font-size: 0.95rem;
}

select,
input[type="number"],
input[type="text"] {
  width: 100%;
  min-height: 42px;
  padding: 8px 10px;
  border: 1px solid var(--line);
  background: #fff;
  color: var(--ink);
  font: inherit;
}

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

.band {
  padding: clamp(44px, 7vw, 86px) clamp(18px, 5vw, 64px);
  border-top: 1px solid var(--line);
}

.band:nth-of-type(even) {
  background: #fff;
}

.section-head {
  max-width: 860px;
  margin-bottom: 26px;
}

.section-head h2,
.split h2 {
  margin: 6px 0 10px;
  font-size: clamp(1.8rem, 3vw, 3rem);
  line-height: 1.08;
}

.section-head p,
.split p,
.explain-block {
  color: var(--muted);
}

.roadmap-layout {
  display: grid;
  grid-template-columns: minmax(280px, 0.8fr) minmax(320px, 1.2fr);
  gap: 20px;
}

.chapter-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(112px, 1fr));
  gap: 10px;
  align-content: start;
}

.chapter-tile {
  min-height: 78px;
  padding: 11px;
  border: 1px solid var(--line);
  background: #fff;
  text-align: left;
  cursor: pointer;
}

.chapter-tile.active {
  border-color: var(--blue);
  background: #edf5ff;
}

.chapter-tile span {
  display: block;
  color: var(--muted);
  font-size: 0.78rem;
}

.chapter-tile strong {
  display: block;
  margin-top: 4px;
  font-size: 0.93rem;
  line-height: 1.18;
}

.detail-panel {
  min-height: 330px;
  padding: clamp(20px, 3vw, 34px);
}

.detail-panel h3 {
  margin: 0 0 10px;
  font-size: clamp(1.5rem, 2vw, 2.2rem);
}

.detail-panel dl {
  display: grid;
  gap: 13px;
  margin: 20px 0 0;
}

.detail-panel dt {
  color: var(--blue);
  font-weight: 760;
}

.detail-panel dd {
  margin: 2px 0 0;
  color: var(--muted);
}

.split {
  display: grid;
  grid-template-columns: minmax(280px, 0.82fr) minmax(320px, 1.18fr);
  gap: clamp(22px, 5vw, 60px);
  align-items: center;
}

.mode-switch {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin: 22px 0;
}

.mode,
.quiz-card button {
  min-height: 42px;
  padding: 9px 13px;
  border: 1px solid var(--line);
  background: #fff;
  cursor: pointer;
}

.mode.active,
.quiz-card button.selected {
  border-color: var(--green);
  background: #edf8f4;
}

.constraint-mode {
  min-height: 42px;
  padding: 9px 13px;
  border: 1px solid var(--line);
  background: #fff;
  cursor: pointer;
}

.constraint-mode.active {
  border-color: var(--green);
  background: #edf8f4;
}

.explain-block {
  padding: 18px;
  border-left: 4px solid var(--green);
  background: #f4faf7;
}

.mechanism-diagram {
  padding: 16px;
}

.mech-link {
  stroke: var(--ink);
  stroke-width: 12;
  stroke-linecap: round;
}

.mech-joint {
  fill: #fff;
  stroke: var(--blue);
  stroke-width: 4;
}

.mech-base {
  fill: #d9e2ea;
}

.mech-note {
  fill: var(--muted);
  font-size: 14px;
  font-weight: 700;
}

.space-lab {
  display: grid;
  grid-template-columns: repeat(2, minmax(280px, 1fr));
  gap: 20px;
}

.plot {
  padding: 18px;
}

.plot h3 {
  margin: 0 0 12px;
}

canvas {
  width: 100%;
  border: 1px solid var(--line);
  background: #fbfdff;
}

.plot p {
  min-height: 48px;
  color: var(--muted);
}

.chapter-hero {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(300px, 0.62fr);
  gap: clamp(22px, 5vw, 64px);
  align-items: center;
  padding: clamp(56px, 8vw, 108px) clamp(18px, 5vw, 64px);
  border-top: 1px solid var(--line);
  background:
    linear-gradient(115deg, rgba(42, 140, 109, 0.13), rgba(255, 255, 255, 0.8) 45%),
    #fff;
}

.chapter3-hero {
  background:
    linear-gradient(115deg, rgba(35, 100, 170, 0.13), rgba(255, 255, 255, 0.83) 46%),
    #fff;
}

.chapter4-hero {
  background:
    linear-gradient(115deg, rgba(211, 155, 37, 0.16), rgba(255, 255, 255, 0.84) 46%),
    #fff;
}

.chapter5-hero {
  background:
    linear-gradient(115deg, rgba(184, 74, 58, 0.13), rgba(255, 255, 255, 0.84) 46%),
    #fff;
}

.chapter6-hero {
  background:
    linear-gradient(115deg, rgba(110, 91, 191, 0.13), rgba(255, 255, 255, 0.84) 46%),
    #fff;
}

.chapter7-hero {
  background:
    linear-gradient(115deg, rgba(42, 140, 109, 0.14), rgba(255, 255, 255, 0.84) 46%),
    #fff;
}

.chapter8-hero {
  background:
    linear-gradient(115deg, rgba(211, 155, 37, 0.16), rgba(255, 255, 255, 0.84) 46%),
    #fff;
}

.chapter9-hero {
  background:
    linear-gradient(115deg, rgba(35, 100, 170, 0.13), rgba(255, 255, 255, 0.84) 46%),
    #fff;
}

.chapter10-hero {
  background:
    linear-gradient(115deg, rgba(42, 140, 109, 0.13), rgba(255, 255, 255, 0.84) 46%),
    #fff;
}

.chapter11-hero {
  background:
    linear-gradient(115deg, rgba(184, 74, 58, 0.12), rgba(255, 255, 255, 0.84) 46%),
    #fff;
}

.chapter12-hero {
  background:
    linear-gradient(115deg, rgba(211, 155, 37, 0.14), rgba(255, 255, 255, 0.84) 46%),
    #fff;
}

.chapter13-hero {
  background:
    linear-gradient(115deg, rgba(35, 100, 170, 0.12), rgba(255, 255, 255, 0.84) 46%),
    #fff;
}

.appendixA-hero {
  background:
    linear-gradient(115deg, rgba(42, 140, 109, 0.12), rgba(255, 255, 255, 0.84) 46%),
    #fff;
}

.appendixB-hero {
  background:
    linear-gradient(115deg, rgba(110, 91, 191, 0.12), rgba(255, 255, 255, 0.84) 46%),
    #fff;
}

.appendixC-hero {
  background:
    linear-gradient(115deg, rgba(211, 155, 37, 0.13), rgba(255, 255, 255, 0.84) 46%),
    #fff;
}

.appendixD-hero {
  background:
    linear-gradient(115deg, rgba(184, 74, 58, 0.12), rgba(255, 255, 255, 0.84) 46%),
    #fff;
}

.chapter-hero > *,
.roadmap-layout > *,
.split > *,
.dof-lab > *,
.calc-grid > *,
.topology-lab > *,
.space-lab > * {
  min-width: 0;
}

.chapter-hero h2 {
  margin: 8px 0 16px;
  max-width: 880px;
  font-size: clamp(2.5rem, 6vw, 6.4rem);
  line-height: 0.98;
  letter-spacing: 0;
}

.chapter-hero p {
  max-width: 840px;
  color: var(--muted);
  font-size: clamp(1rem, 1.5vw, 1.18rem);
}

.formula-panel {
  padding: clamp(20px, 3vw, 34px);
}

.formula-panel strong {
  display: block;
  margin: 8px 0 12px;
  font-size: clamp(1.7rem, 3vw, 2.8rem);
  line-height: 1.08;
  overflow-wrap: anywhere;
}

.dof-lab,
.calc-grid,
.topology-lab,
.motion-lab {
  display: grid;
  grid-template-columns: minmax(280px, 0.72fr) minmax(340px, 1.28fr);
  gap: 20px;
  align-items: stretch;
}

.control-panel,
.visual-panel {
  padding: 18px;
}

.control-panel {
  display: grid;
  gap: 16px;
  align-content: start;
}

.control-panel label {
  display: grid;
  grid-template-columns: 1fr;
  gap: 8px;
  font-weight: 720;
}

.number-readout {
  padding: 16px;
  border: 1px solid var(--line);
  background: #fbfdff;
}

.number-readout strong {
  display: block;
  margin-bottom: 4px;
  color: var(--blue);
  font-size: 2.1rem;
  line-height: 1;
}

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

.chip {
  padding: 7px 10px;
  border: 1px solid var(--line);
  background: #fff;
  color: var(--muted);
  font-size: 0.88rem;
  font-weight: 700;
}

.visual-panel canvas {
  height: auto;
}

.matrix-readout {
  display: grid;
  gap: 10px;
  padding: 16px;
  border: 1px solid var(--line);
  background: #fbfdff;
  color: var(--muted);
  overflow-x: auto;
}

.matrix-readout strong {
  color: var(--ink);
}

.matrix-readout p {
  margin: 0;
}

.mini-matrix {
  width: max-content;
  border-collapse: collapse;
  color: var(--ink);
  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", monospace;
  font-size: 0.9rem;
}

.mini-matrix td {
  min-width: 58px;
  padding: 6px 10px;
  border: 1px solid var(--line);
  text-align: right;
  background: #fff;
}

.formula-panel.compact strong {
  font-size: clamp(1.2rem, 2.1vw, 1.9rem);
}

.joint-table-wrap {
  overflow-x: auto;
}

.joint-table {
  width: 100%;
  min-width: 620px;
  border-collapse: collapse;
}

.joint-table th,
.joint-table td {
  padding: 12px 14px;
  border-bottom: 1px solid var(--line);
  text-align: left;
  vertical-align: top;
}

.joint-table th {
  color: var(--blue);
  font-size: 0.84rem;
  text-transform: uppercase;
}

.joint-table td {
  color: var(--muted);
}

.joint-table td:first-child {
  color: var(--ink);
  font-weight: 760;
}

.preset-row {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.preset {
  min-height: 38px;
  padding: 8px 10px;
  border: 1px solid var(--line);
  background: #fff;
  cursor: pointer;
}

.concept-grid,
.task-cards,
.comparison-grid,
.poe-steps {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 16px;
}

.concept-card,
.task-card {
  padding: 18px;
}

.concept-card h3,
.task-card h3 {
  margin: 0 0 8px;
}

.concept-card p,
.task-card p {
  margin: 0;
  color: var(--muted);
}

.task-card dl {
  display: grid;
  gap: 10px;
  margin: 14px 0 0;
}

.task-card dt {
  color: var(--blue);
  font-weight: 760;
}

.task-card dd {
  margin: 0;
  color: var(--muted);
}

.pipeline {
  display: grid;
  gap: 10px;
  padding: 18px;
}

.pipe-step {
  display: grid;
  grid-template-columns: 44px 1fr;
  gap: 12px;
  align-items: center;
  min-height: 72px;
  padding: 12px;
  border: 1px solid var(--line);
  background: #fff;
}

.poe-step {
  align-items: start;
}

.pipe-step b {
  display: grid;
  place-items: center;
  width: 38px;
  height: 38px;
  color: #fff;
  background: var(--blue);
}

.pipe-step h3,
.pipe-step p {
  margin: 0;
}

.quiz {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 16px;
}

.quiz-card {
  padding: 18px;
}

.quiz-card h3 {
  margin: 0 0 12px;
  font-size: 1.05rem;
}

.answers {
  display: grid;
  gap: 8px;
}

.feedback {
  min-height: 48px;
  margin: 12px 0 0;
  color: var(--muted);
}

footer {
  padding: 26px clamp(18px, 5vw, 64px) 42px;
  color: var(--muted);
  border-top: 1px solid var(--line);
  background: #fff;
}

code {
  padding: 2px 5px;
  background: #eef3f7;
}

.code-card {
  padding: 18px;
  border: 1px solid var(--line);
  background: var(--panel);
  box-shadow: var(--shadow);
  overflow-x: auto;
}

.code-card pre {
  margin: 0;
}

.code-card code {
  display: block;
  min-width: 520px;
  padding: 0;
  background: transparent;
  color: var(--ink);
  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, "Liberation Mono", monospace;
  font-size: 0.92rem;
  line-height: 1.55;
}

@media (max-width: 900px) {
  .topbar,
  .hero,
  .roadmap-layout,
  .split,
  .space-lab,
  .chapter-hero,
  .dof-lab,
  .calc-grid,
  .topology-lab,
  .motion-lab {
    grid-template-columns: 1fr;
  }

  .topbar {
    position: static;
    align-items: flex-start;
  }

  .topbar > * {
    min-width: 0;
  }

  nav {
    width: 100%;
    justify-content: flex-start;
  }

  nav {
    justify-content: flex-start;
  }

  .hero {
    min-height: auto;
  }
}

@media (max-width: 560px) {
  .topbar {
    display: block;
  }

  nav {
    margin-top: 12px;
  }

  label {
    grid-template-columns: 1fr auto;
  }

  label input {
    grid-column: 1 / -1;
  }
}