:root {
  --bg: #f5f8fb;
  --surface: #ffffff;
  --surface-2: #eef6fb;
  --text: #163047;
  --muted: #5d7588;
  --line: #d7e4ee;
  --accent: #0b79b7;
  --accent-2: #0f4c75;
  --accent-soft: #dff2fb;
  --success: #1f8a5a;
  --warning: #b67000;
  --danger: #c93b3b;
  --shadow: 0 12px 32px rgba(10, 38, 64, 0.08);
  --radius: 18px;
  --radius-sm: 12px;
  --code-bg: #0d2335;
  --code-text: #edf7ff;
  --font-stack: -apple-system, BlinkMacSystemFont, "Segoe UI", Helvetica, Arial, sans-serif;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body.course-body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-stack);
  line-height: 1.7;
}

a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

.container {
  width: min(1200px, calc(100vw - 32px));
  margin: 0 auto;
}

.site-header {
  background: #fafdff;
  border-bottom: 1px solid var(--line);
  position: sticky;
  top: 0;
  z-index: 20;
}

.header-inner {
  min-height: 68px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
}

.brand {
  color: var(--text);
  font-weight: 700;
  letter-spacing: 0.02em;
}

.header-nav {
  display: flex;
  align-items: center;
  gap: 16px;
  font-size: 0.95rem;
}

.header-nav a { color: var(--muted); }

.breadcrumb-wrap {
  padding: 14px 0 10px;
}

.breadcrumb {
  color: var(--muted);
  font-size: 0.92rem;
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  align-items: center;
}

.breadcrumb .sep { color: #96aebf; }

.course-layout {
  display: grid;
  grid-template-columns: 320px minmax(0, 1fr);
  gap: 24px;
  align-items: start;
  padding-bottom: 48px;
}

.course-sidebar {
  min-width: 0;
}

.sidebar-sticky {
  position: sticky;
  top: 96px;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 22px;
}

.sidebar-brand {
  color: var(--muted);
  font-size: 0.82rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  margin-bottom: 4px;
}

.course-sidebar h2 {
  margin: 0 0 10px;
  font-size: 1.2rem;
  line-height: 1.35;
}

.sidebar-subtitle {
  margin: 0 0 18px;
  color: var(--muted);
  font-size: 0.93rem;
}

.sidebar-total {
  border: 1px solid var(--line);
  background: var(--surface-2);
  border-radius: var(--radius-sm);
  padding: 14px 16px;
  display: grid;
  gap: 4px;
  margin-bottom: 16px;
}

.sidebar-total span,
.status-card span,
.metric-card span { color: var(--muted); font-size: 0.88rem; }

.sidebar-total strong,
.status-card strong,
.metric-card strong {
  font-size: 1.25rem;
  line-height: 1.2;
}

.sidebar-actions {
  display: grid;
  gap: 10px;
  margin-bottom: 18px;
}

.button,
button,
.question-actions button {
  appearance: none;
  border: 0;
  cursor: pointer;
  border-radius: 999px;
  background: var(--accent);
  color: #fff;
  font-weight: 700;
  font-size: 0.95rem;
  padding: 12px 18px;
  text-align: center;
  box-shadow: 0 8px 18px rgba(11, 121, 183, 0.18);
}

.button:hover,
button:hover,
.question-actions button:hover { filter: brightness(1.05); text-decoration: none; }

.button-secondary {
  background: var(--accent-2);
  box-shadow: 0 8px 18px rgba(15, 76, 117, 0.18);
}

.button-ghost,
.question-actions .button-ghost {
  background: #fff;
  color: var(--text);
  border: 1px solid var(--line);
  box-shadow: none;
}

.sidebar-chapter-list {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  gap: 8px;
}

.sidebar-chapter a {
  display: grid;
  gap: 8px;
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  background: #fff;
  padding: 12px 14px;
  color: inherit;
}

.sidebar-chapter.is-current a {
  border-color: rgba(11, 121, 183, 0.34);
  background: var(--accent-soft);
}

.sidebar-chapter-main {
  display: flex;
  gap: 10px;
  align-items: flex-start;
  font-weight: 700;
  line-height: 1.4;
}

.sidebar-index {
  flex: 0 0 auto;
  width: 26px;
  height: 26px;
  display: inline-grid;
  place-items: center;
  border-radius: 999px;
  background: var(--surface-2);
  color: var(--accent-2);
  font-size: 0.85rem;
  margin-top: 1px;
}

.sidebar-progress {
  color: var(--muted);
  font-size: 0.88rem;
}

.course-main {
  min-width: 0;
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: 22px;
}

.page-meta {
  align-self: start;
  display: inline-flex;
  gap: 8px;
  flex-wrap: wrap;
  color: var(--muted);
  background: #eef6fb;
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: 10px 16px;
  font-size: 0.92rem;
}

h1 {
  margin: 0;
  line-height: 1.2;
  font-size: clamp(1.8rem, 3vw, 2.6rem);
}

h2 {
  margin: 0 0 12px;
  font-size: 1.35rem;
  line-height: 1.35;
}

h3 {
  margin: 0 0 10px;
  font-size: 1.1rem;
  line-height: 1.35;
}

p, li, td, th, label, details, summary {
  font-size: 0.98rem;
}

.page-lead {
  margin: 0;
  color: var(--muted);
  font-size: 1.05rem;
}

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

.status-card {
  border: 1px solid var(--line);
  background: var(--surface);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 16px 18px;
  display: grid;
  gap: 4px;
}

.status-card small,
.metric-card small,
.chart-caption,
.sim-caption {
  color: var(--muted);
  font-size: 0.88rem;
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
}

.noscript-box {
  padding: 14px 16px;
  border: 1px solid rgba(182, 112, 0, 0.3);
  background: #fff8e8;
  color: #744800;
  border-radius: var(--radius-sm);
}

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

.chapter-card {
  display: grid;
  gap: 12px;
  background: var(--surface);
  color: inherit;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 18px;
}

.chapter-card-top {
  display: flex;
  gap: 12px;
  align-items: flex-start;
}

.chapter-card-index {
  flex: 0 0 auto;
  width: 34px;
  height: 34px;
  border-radius: 999px;
  display: inline-grid;
  place-items: center;
  background: var(--accent-soft);
  color: var(--accent-2);
  font-weight: 700;
}

.chapter-card p {
  margin: 0;
  color: var(--muted);
}

.chapter-card-foot {
  display: flex;
  justify-content: space-between;
  align-items: center;
  color: var(--muted);
}

.content-section {
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 22px;
}

.content-section > :last-child { margin-bottom: 0; }

.figure-card {
  margin-top: 18px;
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  background: linear-gradient(180deg, #fbfeff 0%, #f2f8fd 100%);
  overflow: hidden;
}

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

.figure-title { font-size: 22px; fill: #163047; font-weight: 700; }
.figure-caption { font-size: 14px; fill: #496277; }
.figure-label { font-size: 14px; fill: #163047; font-weight: 600; }
.figure-mini { font-size: 13px; fill: #163047; }
.figure-note { font-size: 13px; fill: #496277; }
.sensor-dot { fill: #0b79b7; opacity: 0.95; }
.target-block { fill: #2f516b; opacity: 0.95; }
.arrow-light { stroke: #f0b400; stroke-width: 6; stroke-linecap: round; }
.arrow-radio { stroke: #8a73d6; stroke-width: 6; stroke-linecap: round; }
.arrow-sound { stroke: #0b79b7; stroke-width: 6; stroke-linecap: round; }
.arrow-echo { stroke: #d05488; stroke-width: 6; stroke-linecap: round; }
.dim-line { stroke: #456a86; stroke-width: 2; }
.timeline { stroke: #456a86; stroke-width: 3; stroke-linecap: round; }
.timeline-node { fill: #0b79b7; }
.panel-box { fill: #f7fbfe; stroke: #d7e4ee; stroke-width: 2; }
.panel-title { font-size: 18px; fill: #163047; font-weight: 700; }
.axis-line { stroke: #456a86; stroke-width: 2.5; stroke-linecap: round; }
.wavefront { fill: none; stroke: #0b79b7; stroke-width: 3; stroke-dasharray: 10 8; }
.bar-bg { fill: #f1f6fb; stroke: #d7e4ee; }
.bar-sl { fill: #8bd0ff; }
.bar-rl { fill: #1b80b8; }
.bar-nl { fill: #b5cadd; }

.badge-row {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

.badge-row span {
  border: 1px solid var(--line);
  background: var(--surface-2);
  color: var(--accent-2);
  border-radius: 999px;
  padding: 8px 12px;
  font-size: 0.9rem;
  font-weight: 700;
}

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

.formula-list > div {
  border: 1px solid var(--line);
  background: #fbfeff;
  border-radius: var(--radius-sm);
  padding: 14px 16px;
  display: grid;
  gap: 6px;
}

.formula-list code {
  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  font-size: 0.98rem;
  background: transparent;
}

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

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

.compare-grid > div {
  border: 1px solid var(--line);
  background: #fbfeff;
  border-radius: var(--radius-sm);
  padding: 16px;
}

.key-table {
  width: 100%;
  border-collapse: collapse;
}

.key-table th,
.key-table td {
  border-bottom: 1px solid var(--line);
  padding: 12px 10px;
  text-align: left;
  vertical-align: top;
}

.key-table th {
  color: var(--muted);
  font-weight: 700;
  background: #fbfeff;
}

.bullet-list,
.ordered-list {
  margin: 0;
  padding-left: 20px;
}

.practice-section {
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 22px;
  display: grid;
  gap: 18px;
}

.question {
  border: 1px solid var(--line);
  background: #fbfeff;
  border-radius: var(--radius-sm);
  padding: 16px;
  display: grid;
  gap: 14px;
}

.question-head {
  display: flex;
  justify-content: space-between;
  gap: 10px;
  align-items: center;
  flex-wrap: wrap;
}

.question-kicker {
  color: var(--muted);
  font-size: 0.88rem;
}

.question-status {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 6px 10px;
  border-radius: 999px;
  font-size: 0.85rem;
  font-weight: 700;
  background: #edf4f8;
  color: var(--muted);
}

.question-status.is-correct {
  background: #e8fbf0;
  color: var(--success);
}

.question-status.is-wrong {
  background: #fff1f1;
  color: var(--danger);
}

.question-body p:first-child,
.question-body ul:first-child { margin-top: 0; }

.choice-list {
  border: 0;
  margin: 0;
  padding: 0;
  display: grid;
  gap: 10px;
}

.choice-option {
  display: flex;
  gap: 12px;
  align-items: flex-start;
  border: 1px solid var(--line);
  border-radius: 14px;
  background: #fff;
  padding: 12px 14px;
}

.choice-option input { margin-top: 3px; }

.number-input-wrap {
  display: grid;
  gap: 8px;
  max-width: 320px;
}

.number-input-wrap input {
  width: 100%;
  border: 1px solid var(--line);
  border-radius: 14px;
  padding: 12px 14px;
  font-size: 1rem;
  color: var(--text);
  background: #fff;
}

.question-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

.question-feedback {
  min-height: 1.5em;
  margin: 0;
  font-weight: 700;
}

.question-feedback.is-correct { color: var(--success); }
.question-feedback.is-wrong { color: var(--danger); }

.hint-box {
  border: 1px solid var(--line);
  border-radius: 14px;
  background: #fff;
  padding: 10px 12px;
}

.hint-box summary {
  cursor: pointer;
  font-weight: 700;
  color: var(--accent-2);
}

.hint-box > div,
.hint-box > p {
  margin-top: 10px;
  color: var(--text);
}

.pager {
  display: flex;
  justify-content: space-between;
  gap: 12px;
  flex-wrap: wrap;
}

.pager-link {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  border: 1px solid var(--line);
  background: var(--surface);
  border-radius: 999px;
  padding: 12px 16px;
  box-shadow: var(--shadow);
  color: var(--text);
}

.reference-list {
  margin: 0;
  padding-left: 20px;
}

.reference-list li + li { margin-top: 8px; }

.simulator-shell {
  display: grid;
  grid-template-columns: 360px minmax(0, 1fr);
  gap: 18px;
  align-items: start;
}

.sim-controls,
.sim-results {
  display: grid;
  gap: 16px;
}

.preset-row {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

.preset-btn {
  background: var(--surface-2);
  color: var(--text);
  border: 1px solid var(--line);
  box-shadow: none;
}

.control-grid {
  display: grid;
  gap: 12px;
}

.control-grid label {
  display: grid;
  gap: 8px;
  border: 1px solid var(--line);
  background: #fff;
  border-radius: 14px;
  padding: 12px;
}

.control-grid label span:first-child {
  color: var(--muted);
  font-size: 0.88rem;
}

.control-grid input[type="range"] {
  width: 100%;
}

.control-grid output {
  font-weight: 700;
  font-size: 0.95rem;
}

.control-grid select {
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 10px 12px;
  font-size: 0.95rem;
  color: var(--text);
  background: #fff;
}

.metric-grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 12px;
}

.metric-card {
  border: 1px solid var(--line);
  background: #fff;
  border-radius: 16px;
  padding: 14px 16px;
  display: grid;
  gap: 4px;
}

.gauge-stack {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 12px;
}

.gauge-card,
.chart-card,
.sim-note {
  border: 1px solid var(--line);
  background: #fff;
  border-radius: 16px;
  padding: 16px;
}

.gauge {
  position: relative;
  overflow: hidden;
  height: 16px;
  border-radius: 999px;
  background: linear-gradient(90deg, #f6e3e3 0%, #fff5d8 50%, #e2f5ec 100%);
  margin: 12px 0 8px;
}

.gauge-fill {
  position: absolute;
  inset: 0 auto 0 0;
  width: 0%;
  background: rgba(11, 121, 183, 0.22);
  border-right: 2px solid #0b79b7;
  transition: width 120ms linear;
}

.chart-card canvas {
  width: 100%;
  height: auto;
  border: 1px solid var(--line);
  border-radius: 12px;
  background: #fbfeff;
}

.sim-note {
  color: var(--text);
  background: #f8fbff;
}

.code-block {
  margin: 0;
  overflow: auto;
  border-radius: 16px;
  background: var(--code-bg);
  color: var(--code-text);
  padding: 18px;
  box-shadow: inset 0 0 0 1px rgba(255,255,255,0.05);
}

.code-block code {
  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  font-size: 0.92rem;
  line-height: 1.55;
}

.site-footer {
  border-top: 1px solid var(--line);
  padding: 24px 0 40px;
  background: #fafdff;
}

.footer-inner {
  display: grid;
  gap: 8px;
  color: var(--muted);
  font-size: 0.92rem;
}

.footer-inner a { margin-right: 10px; }

@media (max-width: 1024px) {
  .course-layout,
  .simulator-shell {
    grid-template-columns: minmax(0, 1fr);
  }

  .sidebar-sticky {
    position: static;
  }

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

@media (max-width: 760px) {
  .container {
    width: min(100vw - 20px, 1200px);
  }

  .header-inner {
    min-height: 60px;
    align-items: flex-start;
    flex-direction: column;
    padding: 10px 0;
  }

  .status-grid,
  .chapter-card-grid,
  .compare-grid,
  .gauge-stack,
  .metric-grid {
    grid-template-columns: 1fr;
  }

  .hero-actions,
  .question-actions {
    flex-direction: column;
  }

  .question-actions button,
  .hero-actions .button,
  .hero-actions button {
    width: 100%;
  }

  .content-section,
  .practice-section,
  .sidebar-sticky {
    padding: 16px;
  }
}