/* Native editorial layout. Paper and charcoal with an ink-blue accent; 8px interactive radius. Header is the only sticky layer. */
:root {
  color-scheme: light dark;
  --bg: #f6f2e9;
  --surface: #eee9df;
  --card: #faf7f0;
  --text: #292a2c;
  --muted: #66645f;
  --line: #dcd6cb;
  --accent: #344d67;
  --accent-hover: #273e56;
  --on-accent: #f6f2e9;
  --code: #ede9e1;
  font-family:
    -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC",
    "Microsoft YaHei", sans-serif;
  font-synthesis: none;
  scroll-behavior: smooth;
  scroll-padding-top: 96px;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #202123;
    --surface: #28292c;
    --card: #2b2c2f;
    --text: #e6e2da;
    --muted: #b5b1a9;
    --line: #414145;
    --accent: #b3c5dd;
    --accent-hover: #d2ddeb;
    --on-accent: #202123;
    --code: #252628;
  }
}
:root[data-theme="dark"] {
  color-scheme: dark;
  --bg: #202123;
  --surface: #28292c;
  --card: #2b2c2f;
  --text: #e6e2da;
  --muted: #b5b1a9;
  --line: #414145;
  --accent: #b3c5dd;
  --accent-hover: #d2ddeb;
  --on-accent: #202123;
  --code: #252628;
}
:root[data-theme="light"] {
  color-scheme: light;
}
html[lang="zh-CN"] [lang="en"],
html[lang="en"] [lang="zh-CN"] {
  display: none;
}
* {
  box-sizing: border-box;
}
body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-size: 16px;
  line-height: 1.7;
}
a {
  color: var(--accent);
  text-underline-offset: 5px;
}
a:hover {
  color: var(--accent-hover);
}
button,
a {
  -webkit-tap-highlight-color: transparent;
}
button {
  font: inherit;
  cursor: pointer;
}
button[hidden] {
  display: none;
}
button:focus-visible,
a:focus-visible,
summary:focus-visible,
pre:focus-visible {
  outline: 3px solid var(--accent);
  outline-offset: 5px;
}
button:active,
.button:active {
  transform: translateY(1px);
}
h1,
h2,
h3,
p {
  margin: 0;
}
h1,
h2,
h3 {
  text-wrap: balance;
}
h2 {
  font-size: clamp(28px, 3.2vw, 40px);
  line-height: 1.3;
  letter-spacing: -0.035em;
}
h3 {
  font-size: 20px;
  line-height: 1.4;
  font-weight: 650;
}
p {
  color: var(--muted);
}
.container {
  width: min(1200px, calc(100% - 80px));
  margin-inline: auto;
}
.section {
  padding-block: 88px;
}
.section-intro {
  max-width: 730px;
  margin-bottom: 36px;
}
.section-intro p {
  margin-top: 16px;
  max-width: 65ch;
}
.skip-link {
  position: fixed;
  top: -100px;
  left: 20px;
  z-index: 2;
  background: var(--bg);
  padding: 12px;
}
.skip-link:focus {
  top: 12px;
}
.site-header {
  position: sticky;
  top: 0;
  z-index: 1;
  border-bottom: 1px solid var(--line);
  background: var(--bg);
}
.header-inner {
  height: 76px;
  display: flex;
  align-items: center;
  gap: 40px;
}
.brand {
  display: flex;
  align-items: center;
  gap: 12px;
  color: var(--text);
  text-decoration: none;
  line-height: 1.25;
  font-size: 14px;
  font-weight: 650;
  white-space: nowrap;
}
.brand small {
  display: block;
  font-weight: 400;
  font-size: 11px;
  letter-spacing: 0.06em;
  color: var(--muted);
  margin-top: 4px;
}
.brand-mark {
  display: grid;
  place-items: center;
  border: 1px solid var(--accent);
  color: var(--accent);
  width: 38px;
  height: 38px;
  font-size: 16px;
  letter-spacing: -0.07em;
}
.header-inner nav {
  display: flex;
  align-items: center;
  gap: 24px;
  margin-left: auto;
}
.header-inner nav a {
  font-size: 14px;
  text-decoration: none;
  color: var(--muted);
}
.header-inner nav .nav-reader {
  color: var(--on-accent);
  background: var(--accent);
  border-radius: 8px;
  padding: 7px 14px;
  font-weight: 600;
  white-space: nowrap;
}
.header-inner nav .nav-reader:hover { background: var(--accent-hover); }
.preferences {
  display: flex;
  gap: 8px;
  margin-left: auto;
}
.preferences button {
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 5px 12px;
  background: var(--bg);
  color: var(--text);
  font-size: 13px;
  white-space: nowrap;
}
.hero {
  display: grid;
  grid-template-columns: 1.1fr 1fr;
  gap: 52px;
  align-items: center;
  padding-block: 64px 48px;
  min-height: 510px;
}
.eyebrow {
  font-size: 12px;
  color: var(--accent);
  letter-spacing: 0.08em;
  margin-bottom: 20px;
}
.hero h1 {
  font-size: clamp(40px, 4.25vw, 58px);
  line-height: 1.16;
  letter-spacing: -0.045em;
  font-weight: 650;
}
.headline-end {
  display: block;
}
.hero-description {
  margin-top: 24px;
  max-width: 40ch;
  font-size: 18px;
  line-height: 1.7;
}
.hero-actions {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 16px 28px;
  margin-top: 30px;
}
.button {
  display: inline-flex;
  justify-content: center;
  align-items: center;
  gap: 24px;
  padding: 12px 22px;
  border-radius: 8px;
  border: 1px solid var(--accent);
  font-size: 14px;
  font-weight: 600;
  text-decoration: none;
  white-space: nowrap;
}
.hero-actions .primary {
  min-height: 56px;
  padding: 14px 26px;
  font-size: 16px;
}
.primary {
  background: var(--accent);
  color: var(--on-accent);
}
.primary:hover {
  background: var(--accent-hover);
  color: var(--on-accent);
}
.secondary {
  color: var(--accent);
  background: transparent;
}
.text-link {
  font-size: 14px;
  font-weight: 600;
}
.reader-preview {
  display:block;min-width:0;padding:24px 30px 0;background:var(--card);
  border:1px solid var(--line);color:var(--text);text-decoration:none;
}
.reader-preview:hover{color:var(--text);border-color:var(--accent)}
.preview-meta{display:flex;justify-content:space-between;gap:12px;color:var(--muted);font-size:10px;letter-spacing:.08em;border-bottom:1px solid var(--line);padding-bottom:12px;margin-bottom:18px}
.reader-preview h2{font-size:25px;line-height:1.25;font-weight:600;margin-bottom:20px;letter-spacing:-.025em}
.preview-definition,.preview-example{font-family:"Iowan Old Style",Georgia,"Songti SC",serif;font-size:15px;line-height:1.75}
.preview-label{font-family:inherit;color:var(--accent);font-size:12px;font-weight:600;margin-bottom:8px}
.preview-equation{font-family:Georgia,serif;font-size:22px;text-align:center;margin:16px 0;white-space:nowrap}
.preview-equation .katex{font-size:1em}
.preview-equation .katex-display{margin:0}
.preview-assumption{font-size:12px;color:var(--muted)}
.preview-example{margin-top:20px;padding-top:16px;border-top:1px solid var(--line)}
.preview-example h3{font-size:14px;font-weight:600;line-height:1.6}
.preview-path{display:flex;align-items:center;justify-content:space-between;gap:10px;max-width:290px;margin:12px 0;font-size:27px;font-variant-numeric:lining-nums tabular-nums}
.preview-step{display:grid;text-align:center;line-height:1;color:var(--accent);font-size:22px}
.preview-step small{font:10px/1.5 -apple-system,BlinkMacSystemFont,"Segoe UI",sans-serif}
.preview-footer{display:flex;justify-content:space-between;gap:12px;margin-top:20px;padding-block:14px;border-top:1px solid var(--line);font-size:12px;font-weight:600;color:var(--accent)}
.facts {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr 1.4fr;
  border-block: 1px solid var(--line);
  padding-block: 24px;
  gap: 20px;
}
.facts p {
  display: flex;
  gap: 16px;
  align-items: center;
  font-size: 13px;
}
.facts strong {
  font-size: 36px;
  line-height: 1.2;
  font-weight: 500;
  letter-spacing: -0.04em;
  color: var(--text);
}
.facts .fact-language {
  flex-direction: column;
  align-items: flex-start;
  gap: 3px;
}
.fact-language strong {
  font-size: 22px;
  letter-spacing: -0.025em;
}
.books {
  display: grid;
  grid-template-columns: 1.15fr 1fr;
  gap: 18px;
}
.book {
  display: flex;
  min-width: 0;
  min-height: 192px;
  border: 1px solid var(--line);
  color: var(--text);
  text-decoration: none;
  background: var(--card);
}
.book:hover {
  border-color: var(--accent);
  color: var(--text);
}
.book:nth-child(2),
.book:nth-child(3) {
  background: var(--surface);
}
.book-spine {
  writing-mode: vertical-rl;
  transform: rotate(180deg);
  font-size: 10px;
  letter-spacing: 0.12em;
  padding: 20px 13px;
  border-left: 1px solid var(--line);
  color: var(--accent);
  text-align: center;
}
.book-content {
  padding: 26px;
}
.book h3 {
  font-size: 23px;
}
.book p {
  font-size: 14px;
  margin-top: 9px;
}
.book-action {
  display: block;
  font-size: 13px;
  margin-top: 24px;
  color: var(--accent);
}
.section-note {
  font-size: 12px;
  margin-top: 16px;
}
.curriculum {
  background: var(--surface);
}
.route {
  display: grid;
  grid-template-columns: 1fr;
  max-width: 950px;
  gap: 30px;
}
.route article {
  display: grid;
  grid-template-columns: 220px 1fr;
  column-gap: 28px;
  border-top: 1px solid var(--line);
  padding-top: 24px;
}
.route-range {
  grid-row: span 2;
  font-size: 14px;
  color: var(--accent);
}
.route h3 {
  font-size: 21px;
}
.route p {
  margin-top: 9px;
  max-width: 65ch;
  font-size: 15px;
}
.resource-links {
  display: flex;
  flex-wrap: wrap;
  gap: 14px 28px;
  font-size: 14px;
  margin-top: 30px;
}
.project-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0 60px;
}
.project {
  display: flex;
  gap: 24px;
  border-top: 1px solid var(--line);
  padding-block: 26px;
}
.project-number {
  font-family: ui-monospace, monospace;
  color: var(--muted);
  font-size: 12px;
  padding-top: 3px;
}
.project h3 a {
  text-decoration: none;
}
.project h3 a:hover {
  text-decoration: underline;
}
.project p {
  margin-top: 8px;
  font-size: 14px;
}
.capstone {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 40px;
  padding: 36px;
  background: var(--surface);
  margin-top: 28px;
}
.capstone-label {
  font-size: 14px;
  color: var(--accent);
  margin-bottom: 8px;
}
.capstone h3 {
  font-size: 26px;
}
.capstone p:not(.capstone-label) {
  margin-top: 12px;
  max-width: 60ch;
  font-size: 15px;
}
.getting-started {
  border-block: 1px solid var(--line);
}
.setup-grid {
  display: grid;
  grid-template-columns: 0.85fr 1.15fr;
  gap: 64px;
}
.setup-grid > div {
  min-width: 0;
}
.setup-grid p {
  margin-top: 20px;
}
.setup-grid .text-link {
  display: inline-block;
  margin-top: 20px;
}
.environment {
  font-size: 12px;
  max-width: 55ch;
}
.code-panel {
  border: 1px solid var(--line);
  background: var(--code);
  align-self: start;
}
.code-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  border-bottom: 1px solid var(--line);
  padding: 12px 18px;
  color: var(--muted);
  font:
    12px ui-monospace,
    monospace;
}
.code-header button {
  color: var(--accent);
  background: transparent;
  border: 0;
  font-size: 12px;
  padding: 5px;
}
.code-panel pre {
  margin: 0;
  overflow-x: auto;
  padding: 24px 18px;
  font:
    12px/2 ui-monospace,
    SFMono-Regular,
    Consolas,
    monospace;
  max-width: 100%;
  color: var(--text);
}
.code-panel .copy-status {
  font-size: 12px;
  margin: 0;
  padding: 0 18px 12px;
  min-height: 30px;
}
.reference {
  padding-bottom: 70px;
}
.reference-links {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 24px;
  margin-bottom: 48px;
}
.reference-links a {
  font-size: 19px;
  text-decoration: none;
  border-bottom: 1px solid var(--line);
  padding-bottom: 20px;
}
.reference-links a:hover {
  border-color: var(--accent);
}
details {
  border-top: 1px solid var(--line);
  padding-top: 22px;
}
summary {
  cursor: pointer;
  font-size: 14px;
  color: var(--muted);
}
.scope-copy {
  max-width: 75ch;
  font-size: 14px;
  margin-top: 24px;
}
.scope-copy p + p {
  margin-top: 14px;
}
.site-footer {
  border-top: 1px solid var(--line);
  padding-block: 28px 40px;
  display: flex;
  justify-content: space-between;
  gap: 40px;
  font-size: 12px;
}
.site-footer > p:first-child {
  color: var(--text);
  white-space: nowrap;
}
.site-footer span {
  display: block;
  margin-top: 4px;
}
.rights {
  max-width: 55ch;
}
@media (min-width: 768px) {
  .header-inner nav {
    margin-left: auto;
  }
  .preferences {
    margin-left: 0;
  }
}
@media (max-width: 1023px) {
  .container {
    width: calc(100% - 48px);
  }
  .header-inner {
    gap: 22px;
  }
  .header-inner nav {
    gap: 18px;
  }
  .hero {
    gap: 28px;
  }
  .hero h1 {
    font-size: 40px;
  }
  .reader-preview {padding:22px 24px 0;}
  .facts p {
    flex-direction: column;
    align-items: flex-start;
    gap: 6px;
  }
  .setup-grid {
    gap: 30px;
  }
}
@media (max-width: 767px) {
  :root {
    scroll-padding-top: 82px;
  }
  .container {
    width: calc(100% - 32px);
  }
  .header-inner {
    height: 70px;
    gap: 10px;
  }
  .brand {
    font-size: 11px;
    gap: 8px;
  }
  .brand-mark {
    width: 30px;
    height: 30px;
    font-size: 13px;
  }
  .brand small {
    font-size: 10px;
  }
  .header-inner nav {
    display: none;
  }
  .preferences {
    gap: 4px;
  }
  .preferences button {
    font-size: 11px;
    padding: 6px 8px;
  }
  .hero {
    grid-template-columns: 1fr;
    padding-block: 40px 28px;
    gap: 32px;
    min-height: 0;
  }
  .hero h1 {
    font-size: clamp(34px, 8.8vw, 48px);
  }
  .hero-description {
    font-size: 16px;
    max-width: 35ch;
    margin-top: 20px;
  }
  .hero-actions {
    margin-top: 24px;
  }
  .reader-preview {padding:22px 24px 0;}
  .reader-preview h2 {font-size:24px;}
  .facts {
    grid-template-columns: 1fr 1fr;
    gap: 22px;
    padding-block: 22px;
  }
  .facts p {
    flex-direction: row;
    align-items: center;
    gap: 12px;
  }
  .facts strong {
    font-size: 30px;
  }
  .facts .fact-language {
    gap: 3px;
    align-items: flex-start;
  }
  .fact-language strong {
    font-size: 20px;
  }
  .section {
    padding-block: 52px;
  }
  .section-intro {
    margin-bottom: 26px;
  }
  .books {
    grid-template-columns: 1fr;
    gap: 14px;
  }
  .book {
    min-height: 170px;
  }
  .book-content {
    padding: 22px;
  }
  .book h3 {
    font-size: 22px;
  }
  .route article {
    grid-template-columns: 1fr;
    gap: 8px;
    padding-top: 20px;
  }
  .route-range {
    grid-row: auto;
  }
  .route h3 {
    font-size: 20px;
  }
  .route p {
    margin-top: 0;
  }
  .project-grid {
    grid-template-columns: 1fr;
  }
  .project {
    gap: 20px;
    padding-block: 22px;
  }
  .capstone {
    flex-direction: column;
    align-items: flex-start;
    padding: 24px;
    gap: 24px;
  }
  .capstone h3 {
    font-size: 24px;
  }
  .setup-grid {
    grid-template-columns: 1fr;
    gap: 28px;
  }
  .reference-links {
    grid-template-columns: 1fr 1fr;
    gap: 22px;
  }
  .reference-links a {
    font-size: 17px;
  }
  .site-footer {
    flex-direction: column;
    gap: 18px;
    padding-bottom: 28px;
  }
}
@media (max-width: 359px) {
  .brand-mark {
    display: none;
  }
  .preferences button {
    padding-inline: 6px;
  }
  .hero h1 {
    font-size: 31px;
  }
}
@media (prefers-reduced-motion: reduce) {
  :root {
    scroll-behavior: auto;
  }
}
@media (prefers-reduced-motion: no-preference) {
  a,
  button {
    transition:
      color 0.15s,
      background-color 0.15s,
      border-color 0.15s,
      transform 0.15s;
  }
}

.exercise-credit {
  max-width: 75ch;
  margin-bottom: 36px;
}
.exercise-credit h3 {
  font-size: 18px;
  margin-bottom: 12px;
}
.exercise-credit p {
  font-size: 14px;
  margin-bottom: 12px;
}
.exercise-credit > a {
  font-size: 14px;
}
.support-block {
  margin-bottom: 36px;
  scroll-margin-top: 96px;
}
.support-block h3 {
  font-size: 18px;
  margin-bottom: 16px;
}
.support-paths {
  display: grid;
  align-items: start;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 16px;
}
.support-path {
  min-width: 0;
  border: 1px solid var(--line);
  background: var(--card);
  padding: 22px;
}
.support-path h4 {
  margin: 0 0 8px;
  font-size: 16px;
  line-height: 1.4;
}
.support-path p {
  font-size: 14px;
}
.support-actions {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 12px 18px;
  margin-top: 18px;
}
.support-actions .button {
  padding: 9px 14px;
  gap: 8px;
}
.support-note {
  margin-top: 14px;
  font-size: 12px;
}
@media (max-width: 767px) {
  .support-block {
    scroll-margin-top: 82px;
  }
  .support-paths {
    grid-template-columns: 1fr;
  }
}

.payment-codes{margin-top:20px;padding-top:18px}
.payment-codes summary{color:var(--accent);font-weight:600;line-height:1.7}
.payment-grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:18px;margin-top:20px}
.payment-grid figure{margin:0;min-width:0;text-align:center}
.payment-grid figcaption{font-size:13px;font-weight:600;margin-bottom:10px}
.payment-grid img{display:block;width:100%;height:280px;object-fit:contain;background:#fff;border:1px solid var(--line)}
.payment-original{display:inline-block;font-size:12px;margin-top:9px}
.support-path .payment-note{font-size:12px;line-height:1.8;margin-top:16px}
@media(max-width:480px){.payment-grid{grid-template-columns:1fr;gap:24px}.payment-grid figure{width:min(100%,240px);margin-inline:auto}.payment-grid img{height:auto}}