:root {
  --navy-950: #001d35;
  --navy-900: #002a4a;
  --navy-800: #0a3a5d;
  --ink: #102033;
  --muted: #617184;
  --line: #cfdae5;
  --line-soft: #e8eef4;
  --surface: #ffffff;
  --surface-soft: #f6f9fc;
  --surface-code: #f8fafc;
  --accent: #e63220;
  --accent-dark: #b91f13;
  --accent-soft: #fff4f2;
  --blue: #1266c4;
  --green: #087f5b;
  --warning: #9a5b00;
  --code-blue: #075dd1;
  --shadow: 0 10px 30px rgba(8, 36, 59, .08);
  --reader-scale: 1;
  --topbar-height: 68px;
  --sidebar-width: 322px;
  --outline-width: 278px;
}

[data-theme="dark"] {
  --ink: #e8f0f6;
  --muted: #aebdca;
  --line: #30485b;
  --line-soft: #243c50;
  --surface: #0d2436;
  --surface-soft: #122c40;
  --surface-code: #081d2e;
  --accent-soft: #3a1b1b;
  --code-blue: #7fb4ff;
  --shadow: 0 12px 32px rgba(0, 0, 0, .22);
}

* { box-sizing: border-box; }

html {
  scroll-behavior: smooth;
  color-scheme: light;
}

[data-theme="dark"] { color-scheme: dark; }

body {
  margin: 0;
  color: var(--ink);
  background: var(--surface);
  font-family: "Noto Sans TC", "Microsoft JhengHei", "PingFang TC",
               system-ui, -apple-system, sans-serif;
  font-size: calc(16px * var(--reader-scale));
  line-height: 1.75;
  text-rendering: optimizeLegibility;
}

button, input { font: inherit; }
button { color: inherit; }
a { color: var(--blue); }

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

.skip-link {
  position: fixed;
  z-index: 1000;
  top: 8px;
  left: 8px;
  padding: 8px 14px;
  background: white;
  color: var(--navy-950);
  transform: translateY(-150%);
}

.skip-link:focus { transform: translateY(0); }

.topbar {
  position: sticky;
  z-index: 50;
  top: 0;
  height: var(--topbar-height);
  display: grid;
  grid-template-columns: var(--sidebar-width) 1fr auto;
  align-items: center;
  color: white;
  background: var(--navy-950);
  border-bottom: 1px solid rgba(255, 255, 255, .12);
}

.brand {
  display: flex;
  align-items: center;
  gap: 12px;
  height: 100%;
  padding: 0 22px;
  color: white;
  text-decoration: none;
  font-size: 1.16rem;
  font-weight: 720;
  letter-spacing: .01em;
}

.brand-spectrum {
  width: 58px;
  fill: none;
  stroke: white;
  stroke-width: 2.4;
  stroke-linecap: round;
}

.brand-spectrum path {
  filter: drop-shadow(17px 0 0 #e63220);
}

.course-categories {
  display: flex;
  align-items: center;
  gap: 3px;
  min-width: 0;
  overflow: hidden;
}

.course-categories button,
.reader-tools button {
  border: 0;
  background: transparent;
  color: inherit;
  cursor: pointer;
}

.course-categories button {
  min-height: 44px;
  padding: 0 15px;
  color: #dce9f2;
  font-size: .88rem;
  font-weight: 620;
  white-space: nowrap;
}

.course-categories button:hover,
.course-categories button:focus-visible {
  color: white;
  background: rgba(255, 255, 255, .09);
}

.reader-tools {
  display: flex;
  align-items: center;
  gap: 9px;
  padding-right: 20px;
}

.icon-button {
  display: grid;
  place-items: center;
  width: 38px;
  height: 38px;
  border: 1px solid rgba(255, 255, 255, .23) !important;
  border-radius: 5px;
}

.icon-button svg {
  width: 20px;
  height: 20px;
  fill: none;
  stroke: currentColor;
  stroke-width: 1.8;
  stroke-linejoin: round;
}

.font-controls {
  display: flex;
  height: 38px;
  border: 1px solid rgba(255, 255, 255, .23);
  border-radius: 5px;
  overflow: hidden;
}

.font-controls button {
  width: 38px;
  border-right: 1px solid rgba(255, 255, 255, .18);
  font-size: .78rem;
}

.font-controls button:last-child { border-right: 0; }
.font-controls button:hover { background: rgba(255, 255, 255, .12); }

.overall-progress {
  width: 150px;
  display: grid;
  grid-template-columns: 1fr auto;
  column-gap: 8px;
  font-size: .76rem;
  line-height: 1.3;
}

.overall-progress strong { font-variant-numeric: tabular-nums; }

.progress-track {
  grid-column: 1 / -1;
  height: 6px;
  margin-top: 4px;
  overflow: hidden;
  background: var(--line-soft);
  border-radius: 99px;
}

.progress-track span {
  display: block;
  width: 0;
  height: 100%;
  background: var(--accent);
  border-radius: inherit;
  transition: width .35s ease;
}

.menu-toggle { display: none; }

.app-shell {
  display: grid;
  grid-template-columns: var(--sidebar-width) minmax(520px, 1fr) var(--outline-width);
  min-height: calc(100vh - var(--topbar-height));
}

.curriculum,
.outline {
  position: sticky;
  top: var(--topbar-height);
  height: calc(100vh - var(--topbar-height));
  overflow-y: auto;
  scrollbar-width: thin;
  background: var(--surface);
}

.curriculum {
  border-right: 1px solid var(--line);
  padding: 24px 20px;
}

.curriculum-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.curriculum h2,
.outline h2 {
  margin: 0;
  color: var(--ink);
  font-size: 1rem;
  letter-spacing: .04em;
}

.drawer-close {
  display: none;
  border: 0;
  background: transparent;
  font-size: 1.7rem;
}

.lesson-list {
  position: relative;
  margin: 22px 0 0;
  padding: 0;
  list-style: none;
}

.lesson-list::before {
  content: "";
  position: absolute;
  z-index: 0;
  top: 28px;
  bottom: 28px;
  left: 18px;
  width: 1px;
  background: var(--navy-800);
}

.lesson-item {
  position: relative;
  z-index: 1;
  margin: 0 0 8px;
}

.lesson-link {
  width: 100%;
  min-height: 62px;
  display: grid;
  grid-template-columns: 38px 1fr 18px;
  align-items: center;
  gap: 10px;
  padding: 9px 10px;
  border: 1px solid transparent;
  border-radius: 6px;
  text-align: left;
  background: transparent;
  cursor: pointer;
}

.lesson-link:hover { background: var(--surface-soft); }

.lesson-item.active .lesson-link {
  border-color: #f0b7b1;
  background: var(--accent-soft);
}

.lesson-number {
  display: grid;
  place-items: center;
  width: 34px;
  height: 34px;
  border: 1px solid #9eafbe;
  border-radius: 50%;
  background: var(--surface);
  color: var(--ink);
  font-size: .84rem;
  font-weight: 700;
}

.lesson-item.active .lesson-number,
.lesson-item.completed .lesson-number {
  border-color: var(--accent);
  color: white;
  background: var(--accent);
}

.lesson-name {
  display: block;
  font-size: .84rem;
  font-weight: 660;
  line-height: 1.35;
}

.lesson-duration {
  display: block;
  margin-top: 4px;
  color: var(--muted);
  font-size: .7rem;
}

.lesson-state {
  width: 13px;
  height: 13px;
  border: 1px solid #9eafbe;
  border-radius: 50%;
}

.lesson-item.completed .lesson-state {
  display: grid;
  place-items: center;
  border-color: var(--accent);
  color: white;
  background: var(--accent);
  font-size: 9px;
}

.legend {
  display: flex;
  flex-wrap: wrap;
  gap: 10px 14px;
  margin-top: 24px;
  padding-top: 18px;
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-size: .66rem;
}

.legend span { display: inline-flex; align-items: center; gap: 5px; }
.legend i {
  width: 11px;
  height: 11px;
  border: 1px solid #9eafbe;
  border-radius: 50%;
  font-style: normal;
}
.legend .current-dot { border-color: var(--accent); }
.legend .done-dot {
  display: grid;
  place-items: center;
  color: white;
  border-color: var(--accent);
  background: var(--accent);
  font-size: 8px;
}

.lesson {
  width: min(100%, 960px);
  margin: 0 auto;
  padding: 34px 42px 60px;
  outline: none;
}

.lesson-meta {
  display: flex;
  justify-content: space-between;
  color: var(--navy-800);
  font-size: .84rem;
  font-weight: 660;
}

.lesson-meta span:last-child { font-variant-numeric: tabular-nums; }

.lesson h1 {
  margin: 20px 0 4px;
  font-size: clamp(2rem, 3.3vw, 2.8rem);
  line-height: 1.2;
  letter-spacing: -.02em;
}

.lesson-level {
  margin-bottom: 22px;
  color: var(--muted);
  font-size: .8rem;
}

.objective {
  display: grid;
  grid-template-columns: 44px 1fr;
  gap: 14px;
  padding: 18px 20px;
  border: 1px solid #efb7b0;
  border-radius: 6px;
  background: var(--accent-soft);
}

.objective-icon {
  display: grid;
  place-items: start center;
  color: var(--accent);
}

.objective-icon svg {
  width: 34px;
  height: 34px;
  fill: none;
  stroke: currentColor;
  stroke-width: 2;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.objective h2 {
  margin: 0 0 2px;
  color: var(--accent-dark);
  font-size: .95rem;
}

.objective p { margin: 0; font-size: .9rem; }

.lesson-body {
  margin-top: 30px;
}

.lesson-body section {
  scroll-margin-top: calc(var(--topbar-height) + 24px);
  margin: 0 0 44px;
}

.lesson-body h2 {
  margin: 0 0 14px;
  padding-bottom: 8px;
  border-bottom: 1px solid var(--line);
  font-size: 1.42rem;
  line-height: 1.35;
}

.lesson-body h3 {
  margin: 26px 0 8px;
  color: var(--navy-800);
  font-size: 1.03rem;
}

[data-theme="dark"] .lesson-body h3,
[data-theme="dark"] .lesson-meta { color: #8fc7f0; }

.lesson-body p { margin: 0 0 14px; }
.lesson-body ul,
.lesson-body ol { padding-left: 1.5em; }
.lesson-body li { margin: 7px 0; }
.lesson-body strong { font-weight: 720; }

.lead {
  color: var(--muted);
  font-size: 1.04rem;
}

.visual {
  margin: 22px 0;
  padding: 14px;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: var(--surface);
}

.visual figcaption {
  margin: 0 0 8px;
  font-size: .85rem;
  font-weight: 700;
}

.visual svg {
  display: block;
  width: 100%;
  height: auto;
  min-height: 220px;
}

.chart-grid { stroke: var(--line-soft); stroke-width: 1; }
.chart-axis { stroke: var(--muted); stroke-width: 1.2; }
.chart-line { fill: none; stroke: var(--navy-800); stroke-width: 1.5; opacity: .62; }
.chart-line.accent { stroke: var(--accent); stroke-width: 2.4; opacity: 1; }
.chart-mark { stroke: var(--accent); stroke-width: 1.5; stroke-dasharray: 4 4; }
.chart-text {
  fill: var(--muted);
  font-family: inherit;
  font-size: 12px;
}

.code-block {
  position: relative;
  margin: 18px 0;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: var(--surface-code);
}

.code-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  min-height: 38px;
  padding: 0 9px 0 14px;
  border-bottom: 1px solid var(--line);
  color: var(--muted);
  font-family: ui-monospace, "Cascadia Code", Consolas, monospace;
  font-size: .73rem;
}

.copy-button {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  min-height: 30px;
  padding: 2px 9px;
  border: 1px solid var(--line);
  border-radius: 4px;
  color: var(--ink);
  background: var(--surface);
  cursor: pointer;
  font-family: inherit;
}

.copy-button:hover { border-color: var(--navy-800); }
.copy-button.copied {
  color: white;
  border-color: var(--green);
  background: var(--green);
}

.copy-button svg {
  width: 15px;
  height: 15px;
  fill: none;
  stroke: currentColor;
  stroke-width: 1.8;
}

pre {
  margin: 0;
  overflow-x: auto;
  padding: 17px 20px;
  tab-size: 2;
  font-family: ui-monospace, "Cascadia Code", Consolas, monospace;
  font-size: .84rem;
  line-height: 1.7;
}

code {
  font-family: ui-monospace, "Cascadia Code", Consolas, monospace;
}

p code, li code, td code {
  padding: .12em .32em;
  border: 1px solid var(--line-soft);
  border-radius: 3px;
  color: var(--navy-800);
  background: var(--surface-soft);
  font-size: .88em;
}

[data-theme="dark"] p code,
[data-theme="dark"] li code,
[data-theme="dark"] td code { color: #9dcbff; }

.kw { color: #8d20b5; }
.fn { color: var(--code-blue); }
.st { color: #a64b00; }
.co { color: #6b7c8d; font-style: italic; }
.nu { color: #086b63; }

.callout {
  margin: 20px 0;
  padding: 14px 17px;
  border-left: 4px solid var(--blue);
  background: var(--surface-soft);
}

.callout.warning { border-left-color: #e38a00; }
.callout.success { border-left-color: var(--green); }
.callout strong { display: block; margin-bottom: 3px; }
.callout p:last-child { margin-bottom: 0; }

.formula {
  margin: 18px 0;
  padding: 18px;
  overflow-x: auto;
  text-align: center;
  border-block: 1px solid var(--line);
  font-family: Georgia, "Times New Roman", serif;
  font-size: 1.15rem;
}

.table-wrap {
  margin: 18px 0;
  overflow-x: auto;
  border: 1px solid var(--line);
  border-radius: 6px;
}

table {
  width: 100%;
  border-collapse: collapse;
  font-size: .82rem;
}

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

th {
  color: var(--navy-800);
  background: var(--surface-soft);
  font-weight: 720;
}

[data-theme="dark"] th { color: #9dcbff; }
tr:last-child td { border-bottom: 0; }

.checkpoint {
  margin-top: 30px;
  padding: 20px;
  border: 1px solid var(--line);
  border-radius: 6px;
  box-shadow: var(--shadow);
}

.checkpoint h3 { margin-top: 0; }
.checkpoint-options {
  display: grid;
  gap: 9px;
  margin-top: 14px;
}

.checkpoint-option {
  display: flex;
  align-items: flex-start;
  gap: 10px;
  padding: 10px 12px;
  border: 1px solid var(--line);
  border-radius: 5px;
  background: var(--surface);
  cursor: pointer;
}

.checkpoint-option:hover { border-color: var(--navy-800); }
.checkpoint-option input { margin-top: 6px; accent-color: var(--accent); }

.check-answer {
  min-height: 40px;
  margin-top: 14px;
  padding: 8px 15px;
  border: 1px solid var(--navy-800);
  border-radius: 4px;
  background: transparent;
  cursor: pointer;
  font-weight: 650;
}

.quiz-feedback {
  display: none;
  margin-top: 12px;
  padding: 10px 12px;
  border-left: 4px solid var(--green);
  background: var(--surface-soft);
}

.quiz-feedback.visible { display: block; }
.quiz-feedback.wrong { border-left-color: var(--accent); }

.lesson-actions {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
  padding-top: 24px;
  border-top: 1px solid var(--line);
}

.primary-button,
.secondary-button {
  min-height: 48px;
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 10px;
  border-radius: 5px;
  cursor: pointer;
  font-weight: 680;
}

.primary-button {
  color: white;
  border: 1px solid var(--accent);
  background: var(--accent);
}

.primary-button:hover { background: var(--accent-dark); }

.secondary-button {
  border: 1px solid var(--navy-800);
  background: transparent;
}

.secondary-button.completed {
  color: white;
  border-color: var(--green);
  background: var(--green);
}

.primary-button svg,
.secondary-button svg {
  width: 20px;
  height: 20px;
  fill: none;
  stroke: currentColor;
  stroke-width: 2;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.primary-button svg { fill: currentColor; stroke: none; }

.lesson-pagination {
  display: flex;
  justify-content: space-between;
  margin-top: 22px;
  padding-top: 18px;
  border-top: 1px solid var(--line);
}

.lesson-pagination button {
  min-height: 42px;
  padding: 7px 14px;
  border: 1px solid var(--line);
  border-radius: 4px;
  background: transparent;
  cursor: pointer;
}

.lesson-pagination button:hover:not(:disabled) {
  border-color: var(--navy-800);
}

.lesson-pagination button:disabled {
  opacity: .35;
  cursor: not-allowed;
}

.outline {
  padding: 30px 22px;
  border-left: 1px solid var(--line);
}

.outline > ol {
  margin: 14px 0 30px;
  padding: 0 0 0 14px;
  border-left: 1px solid var(--line);
  list-style: none;
}

.outline > ol li { margin: 0 0 12px; }
.outline > ol a {
  color: var(--muted);
  text-decoration: none;
  font-size: .76rem;
  line-height: 1.35;
}
.outline > ol a:hover { color: var(--accent); }
.outline > ol li:first-child {
  margin-left: -15px;
  padding-left: 14px;
  border-left: 2px solid var(--accent);
}
.outline > ol li:first-child a { color: var(--accent); }

.key-points {
  margin-top: 22px;
  padding-top: 22px;
  border-top: 1px solid var(--line);
}

.key-points ul {
  margin: 14px 0 0;
  padding: 0;
  list-style: none;
}

.key-points li {
  position: relative;
  margin: 11px 0;
  padding-left: 22px;
  color: var(--muted);
  font-size: .72rem;
  line-height: 1.5;
}

.key-points li::before {
  content: "✓";
  position: absolute;
  left: 0;
  top: 1px;
  display: grid;
  place-items: center;
  width: 14px;
  height: 14px;
  border-radius: 50%;
  color: white;
  background: var(--accent);
  font-size: 9px;
  font-weight: 800;
}

.tip {
  margin-top: 25px;
  padding: 13px 14px;
  border: 1px solid #b7d4ee;
  border-radius: 5px;
  background: #f3f9ff;
  font-size: .72rem;
}

[data-theme="dark"] .tip { background: #102d46; }
.tip strong { color: var(--blue); }
.tip p { margin: 5px 0 0; }

.chapter-progress {
  margin-top: 25px;
  padding-top: 22px;
  border-top: 1px solid var(--line);
}

.chapter-progress strong {
  display: block;
  margin-top: 12px;
  font-size: .8rem;
}

footer {
  display: none;
  padding: 24px;
  border-top: 1px solid var(--line);
  color: var(--muted);
  background: var(--surface);
  text-align: center;
  font-size: .72rem;
}

.noscript {
  position: fixed;
  z-index: 1000;
  inset: 20px;
  padding: 20px;
  color: white;
  background: #9b1c1c;
}

@media (max-width: 1180px) {
  :root { --sidebar-width: 276px; --outline-width: 236px; }
  .course-categories button { padding-inline: 9px; font-size: .8rem; }
  .overall-progress { display: none; }
  .lesson { padding-inline: 30px; }
}

@media (max-width: 940px) {
  :root { --topbar-height: 64px; }
  .topbar {
    grid-template-columns: 1fr auto;
  }
  .course-categories,
  .outline { display: none; }
  .reader-tools { padding-right: 14px; }
  .menu-toggle {
    display: grid;
    width: 42px;
    height: 42px;
    place-content: center;
    gap: 5px;
  }
  .menu-toggle span:not(.sr-only) {
    display: block;
    width: 23px;
    height: 2px;
    background: currentColor;
  }
  .app-shell { display: block; }
  .curriculum {
    position: fixed;
    z-index: 80;
    top: 0;
    left: 0;
    width: min(88vw, 340px);
    height: 100vh;
    transform: translateX(-105%);
    transition: transform .25s ease;
    box-shadow: 15px 0 40px rgba(0, 0, 0, .18);
  }
  .curriculum.open { transform: translateX(0); }
  .drawer-close { display: block; cursor: pointer; }
  .drawer-scrim {
    position: fixed;
    z-index: 70;
    inset: 0;
    background: rgba(0, 19, 36, .54);
  }
  .lesson { width: min(100%, 860px); }
}

@media (max-width: 620px) {
  :root { --topbar-height: 78px; }
  .topbar { height: var(--topbar-height); }
  .brand {
    padding-inline: 18px 8px;
    font-size: .98rem;
  }
  .brand-spectrum { width: 43px; }
  .reader-tools { gap: 2px; padding-right: 9px; }
  .font-controls,
  .icon-button { display: none; }
  .lesson {
    padding: 26px 20px 44px;
  }
  .lesson h1 {
    margin-top: 14px;
    font-size: 2rem;
  }
  .lesson-meta { font-size: .76rem; }
  .objective {
    grid-template-columns: 36px 1fr;
    padding: 15px;
  }
  .objective-icon svg { width: 29px; height: 29px; }
  .lesson-body { margin-top: 26px; }
  .lesson-body section { margin-bottom: 36px; }
  .lesson-body h2 { font-size: 1.24rem; }
  .visual { margin-inline: -4px; padding: 8px; }
  .visual svg { min-height: 180px; }
  pre { padding: 15px; font-size: .78rem; }
  .lesson-actions { grid-template-columns: 1fr; }
  .primary-button,
  .secondary-button { min-height: 52px; }
  .lesson-pagination button { min-width: 46%; }
}

@media print {
  .topbar,
  .curriculum,
  .outline,
  .lesson-actions,
  .lesson-pagination,
  footer { display: none !important; }
  .app-shell { display: block; }
  .lesson {
    width: auto;
    max-width: none;
    margin: 0;
    padding: 0;
  }
  .lesson-body section { break-inside: avoid; }
  .code-block,
  .checkpoint,
  .visual { box-shadow: none; break-inside: avoid; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    scroll-behavior: auto !important;
    transition-duration: .01ms !important;
    animation-duration: .01ms !important;
  }
}