:root {
  color-scheme: light;
  --bg: #fff;
  --text: #242b36;
  --muted: #606978;
  --subtle: #f6f7f9;
  --border: #e6e9ee;
  --accent: #087f8c;
  --accent-bg: #e9f5f5;
  --note: #f0f7ff;
  --note-text: #315e86;
  --header: rgba(255, 255, 255, 0.96);
}
:root[data-theme="dark"] {
  color-scheme: dark;
  --bg: #20232b;
  --text: #eef0f5;
  --muted: #afb7c5;
  --subtle: #272b35;
  --border: #373d49;
  --accent: #77d7dc;
  --accent-bg: #243e44;
  --note: #273544;
  --note-text: #b0d2ef;
  --header: rgba(32, 35, 43, 0.96);
}
* {
  box-sizing: border-box;
}
html {
  scroll-behavior: smooth;
  scroll-padding-top: 100px;
}
body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family:
    Inter,
    ui-sans-serif,
    system-ui,
    -apple-system,
    BlinkMacSystemFont,
    "Segoe UI",
    sans-serif;
  font-size: 16px;
  line-height: 1.75;
  -webkit-font-smoothing: antialiased;
}
a {
  color: var(--accent);
  text-decoration: none;
}
a:hover {
  text-decoration: underline;
}
button {
  font: inherit;
}
button,
a,
summary {
  -webkit-tap-highlight-color: transparent;
}
button {
  cursor: pointer;
}
button:focus-visible,
a:focus-visible,
summary:focus-visible {
  outline: 3px solid var(--accent);
  outline-offset: 5px;
  border-radius: 4px;
}
[hidden] {
  display: none !important;
}
.skip-link {
  position: fixed;
  top: -100px;
  left: 16px;
  z-index: 100;
  background: var(--bg);
  padding: 12px 20px;
  border: 2px solid var(--accent);
}
.skip-link:focus {
  top: 8px;
}
.header {
  height: 84px;
  border-bottom: 1px solid var(--border);
  display: flex;
  align-items: center;
  gap: 40px;
  padding: 0 36px;
  position: sticky;
  top: 0;
  background: var(--header);
  backdrop-filter: blur(12px);
  z-index: 10;
}
.brand {
  display: flex;
  align-items: center;
  gap: 12px;
  color: var(--text);
  font-weight: 700;
  font-size: 19px;
  line-height: 1.2;
  letter-spacing: -0.5px;
  white-space: nowrap;
}
.brand:hover {
  text-decoration: none;
}
.brand-caption {
  display: block;
  color: var(--muted);
  font-weight: 400;
  font-size: 12px;
  letter-spacing: 0.2px;
  margin-top: 5px;
}
.top-nav {
  display: flex;
  gap: 9px;
  align-items: center;
  margin-left: auto;
}
.top-nav a {
  padding: 7px 18px;
  border-radius: 22px;
  color: var(--muted);
  font-weight: 600;
  font-size: 15px;
}
.top-nav a:hover {
  text-decoration: none;
  background: var(--subtle);
}
.top-nav a[aria-current] {
  background: var(--accent-bg);
  color: var(--accent);
}
.header-actions {
  display: flex;
  align-items: center;
  gap: 18px;
}
.stage {
  font-size: 12px;
  color: var(--muted);
  border: 1px solid var(--border);
  padding: 2px 10px;
  border-radius: 6px;
}
.icon-button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 40px;
  height: 40px;
  color: var(--muted);
  border: 0;
  background: transparent;
  border-radius: 50%;
  font-size: 26px;
}
.icon-button:hover {
  background: var(--subtle);
  color: var(--text);
}
svg {
  width: 21px;
  height: 21px;
  fill: none;
  stroke: currentColor;
  stroke-width: 1.65;
  stroke-linecap: round;
  stroke-linejoin: round;
}
.menu-toggle {
  display: none;
}
.page-layout {
  display: grid;
  grid-template-columns: 270px minmax(0, 850px) 220px;
  max-width: 1536px;
  margin: auto;
}
.sidebar {
  border-right: 1px solid var(--border);
  position: sticky;
  top: 84px;
  height: calc(100dvh - 84px);
  overflow-y: auto;
  padding: 36px 20px 24px;
}
.sidebar-label {
  font-size: 11px;
  letter-spacing: 1.5px;
  font-weight: 700;
  color: var(--muted);
  margin: 0 0 14px;
  padding-left: 14px;
}
.overview-link {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 10px 14px;
  color: var(--text);
  font-weight: 600;
  font-size: 15px;
  border-radius: 8px;
}
.overview-link[aria-current] {
  background: var(--accent-bg);
  color: var(--accent);
}
.overview-link:hover {
  text-decoration: none;
  background: var(--subtle);
}
.curriculum-label {
  margin-top: 35px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  font-size: 10px;
  letter-spacing: 1px;
}
.curriculum-label span {
  font-weight: 400;
  letter-spacing: 0;
  font-size: 11px;
}
.chapter {
  margin: 13px 0;
}
.chapter summary {
  font-size: 14px;
  font-weight: 600;
  cursor: pointer;
  list-style: none;
  padding: 5px 14px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
}
.chapter summary::-webkit-details-marker {
  display: none;
}
.chapter summary:after {
  content: "›";
  font-size: 20px;
  color: var(--muted);
  line-height: 1;
  transform: rotate(0deg);
}
.chapter[open] summary:after {
  transform: rotate(90deg);
}
.chapter ul {
  list-style: none;
  padding: 0;
  margin: 7px 0 18px 24px;
  border-left: 1px solid var(--border);
}
.chapter li {
  padding: 7px 0 7px 17px;
  font-size: 13px;
  color: var(--muted);
}
.chapter li a {
  display: block;
  padding: 5px 10px;
  margin: -5px 0 -5px -10px;
  border-radius: 6px;
  font-size: 14px;
}
.chapter li a[aria-current="page"] {
  background: var(--accent-bg);
  color: var(--accent);
  font-weight: 600;
}
.sidebar-note {
  display: flex;
  gap: 11px;
  margin: 38px 14px 0;
  padding-top: 22px;
  border-top: 1px solid var(--border);
  color: var(--muted);
  font-size: 12px;
  line-height: 1.7;
}
.sidebar-note p {
  margin: 0;
}
.note-mark {
  font-size: 22px;
  color: var(--accent);
}
main {
  min-width: 0;
  padding: 38px 60px 0;
  outline: none;
}
.breadcrumb {
  display: flex;
  gap: 12px;
  color: var(--accent);
  font-size: 13px;
  font-weight: 600;
  margin-bottom: 24px;
}
.breadcrumb span {
  color: var(--muted);
  font-weight: 400;
}
h1 {
  font-size: 48px;
  line-height: 1.15;
  letter-spacing: -1.8px;
  font-weight: 750;
  margin: 0 0 22px;
}
h2 {
  font-size: 27px;
  line-height: 1.3;
  letter-spacing: -0.6px;
  margin: 0 0 18px;
  font-weight: 700;
}
h3 {
  font-size: 18px;
  line-height: 1.45;
  letter-spacing: -0.2px;
  margin: 0 0 8px;
}
p {
  margin: 0 0 18px;
}
.lead {
  font-size: 22px;
  line-height: 1.55;
  color: var(--muted);
  letter-spacing: -0.3px;
  margin-bottom: 30px;
}
.intro-box {
  padding: 22px 26px;
  background: var(--subtle);
  border-radius: 12px;
  margin: 30px 0 42px;
}
.box-heading {
  display: flex;
  align-items: center;
  gap: 9px;
  font-weight: 700;
  font-size: 16px;
}
.book-icon {
  font-size: 24px;
  color: var(--accent);
  line-height: 1;
}
.intro-box ul {
  margin: 12px 0 0;
  padding-left: 23px;
  font-size: 15px;
}
.intro-box li {
  padding: 3px 0;
}
section {
  margin: 40px 0;
  scroll-margin-top: 108px;
}
.heading-link {
  font-size: 21px;
  opacity: 0;
  margin-left: 10px;
}
h2:hover .heading-link,
.heading-link:focus {
  opacity: 1;
}
.concept-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 16px;
  margin-top: 24px;
}
.concept {
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 23px 22px 18px;
}
.concept-label,
.eyebrow {
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 1.2px;
  color: var(--accent);
}
.concept h3 {
  margin: 12px 0;
  font-size: 18px;
}
.concept p {
  font-size: 14px;
  color: var(--muted);
  line-height: 1.7;
}
.concept-footer {
  border-top: 1px solid var(--border);
  padding-top: 12px;
  display: flex;
  justify-content: space-between;
  color: var(--muted);
  font-size: 12px;
}
.learning-path {
  list-style: none;
  padding: 0;
  margin: 26px 0;
}
.learning-path li {
  display: flex;
  gap: 20px;
  padding: 21px 0;
  border-bottom: 1px solid var(--border);
}
.learning-path li:first-child {
  padding-top: 0;
}
.learning-path li:last-child {
  border-bottom: 0;
}
.step-number {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  width: 35px;
  height: 35px;
  border-radius: 50%;
  font-size: 12px;
  font-weight: 600;
  background: var(--subtle);
  color: var(--muted);
}
.learning-path h3 {
  font-size: 17px;
  margin: 1px 0 5px;
}
.learning-path p {
  font-size: 15px;
  color: var(--muted);
  margin: 0;
}
.progress-note {
  display: flex;
  gap: 15px;
  padding: 23px 25px;
  border-radius: 12px;
  background: var(--note);
  color: var(--note-text);
}
.progress-note h3 {
  font-size: 16px;
}
.progress-note p {
  font-size: 14px;
  margin: 0;
}
.info-icon {
  display: flex;
  border: 1.5px solid currentColor;
  border-radius: 50%;
  width: 19px;
  height: 19px;
  flex-shrink: 0;
  align-items: center;
  justify-content: center;
  font-size: 12px;
  font-weight: 700;
  margin-top: 3px;
}
.next-page {
  display: flex;
  align-items: center;
  justify-content: space-between;
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 20px 24px;
  margin: 40px 0 48px;
  color: var(--text);
}
.next-page:hover {
  border-color: var(--accent);
  text-decoration: none;
  background: var(--subtle);
}
.next-page div span {
  display: block;
  font-size: 10px;
  letter-spacing: 1.4px;
  color: var(--muted);
  margin-bottom: 5px;
}
.next-page strong {
  font-size: 17px;
  font-weight: 600;
}
.next-page > span {
  font-size: 25px;
  color: var(--accent);
}
.page-outline {
  position: sticky;
  top: 84px;
  height: fit-content;
  padding: 43px 25px 20px 10px;
}
.page-outline .sidebar-label {
  padding-left: 14px;
  font-size: 10px;
}
.page-outline nav {
  border-left: 1px solid var(--border);
  display: grid;
}
.page-outline nav a {
  font-size: 12px;
  color: var(--muted);
  padding: 8px 14px;
  border-left: 2px solid transparent;
  margin-left: -1px;
}
.page-outline nav a[aria-current] {
  border-left-color: var(--accent);
  color: var(--accent);
}
.outline-note {
  font-size: 11px;
  line-height: 1.8;
  color: var(--muted);
  margin: 30px 0 0 14px;
}
.curriculum-pagination {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 16px;
  margin: 40px 0 48px;
}
.curriculum-pagination .next-page {
  margin: 0;
  gap: 12px;
}
.curriculum-prev {
  grid-column: 1;
}
.curriculum-next {
  grid-column: 2;
}
@media (max-width: 540px) {
  .curriculum-pagination {
    grid-template-columns: 1fr;
  }
  .curriculum-pagination .next-page {
    grid-column: 1;
  }
}
.page-footer {
  border-top: 1px solid var(--border);
  padding: 23px 0 35px;
  display: flex;
  justify-content: space-between;
  gap: 20px;
  font-size: 11px;
  color: var(--muted);
}
.page-footer span:first-child {
  font-weight: 600;
}
.reference-list {
  display: grid;
  gap: 14px;
}
.reference-list > a {
  padding: 24px;
  border: 1px solid var(--border);
  border-radius: 12px;
  color: var(--text);
}
.reference-list > a:hover {
  border-color: var(--accent);
  background: var(--subtle);
  text-decoration: none;
}
.reference-list h3 {
  margin-top: 9px;
}
.reference-list p {
  color: var(--muted);
  font-size: 15px;
  margin: 0;
}
.author-placeholder {
  padding: 28px;
  background: var(--subtle);
  border: 1px dashed var(--border);
  border-radius: 12px;
}
.author-placeholder p {
  margin: 10px 0 0;
  color: var(--muted);
}
.mobile-navigation {
  background: var(--bg);
  color: var(--text);
  border: 0;
  border-right: 1px solid var(--border);
  margin: 0;
  max-height: 100dvh;
  height: 100dvh;
  max-width: 90vw;
  width: 330px;
  padding: 22px;
}
.mobile-navigation::backdrop {
  background: rgba(10, 15, 25, 0.55);
}
.mobile-heading {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 30px;
}
.not-found {
  max-width: 700px;
  margin: 12vh auto;
  padding: 30px;
}
@media (min-width: 1500px) {
  .page-layout {
    grid-template-columns: 290px minmax(0, 1fr) 240px;
  }
  main {
    padding-left: 80px;
    padding-right: 80px;
  }
}
@media (max-width: 1199px) {
  .page-layout {
    grid-template-columns: 245px minmax(0, 1fr);
  }
  .page-outline {
    display: none;
  }
  main {
    padding-left: 48px;
    padding-right: 48px;
  }
  .header {
    padding: 0 25px;
    gap: 24px;
  }
  .sidebar {
    padding-left: 13px;
    padding-right: 13px;
  }
}
@media (max-width: 800px) {
  .header {
    height: 72px;
    padding: 0 20px;
    gap: 15px;
  }
  .brand {
    font-size: 16px;
  }
  .brand img {
    width: 30px;
    height: 30px;
  }
  .brand-caption {
    font-size: 10px;
  }
  .stage {
    display: none;
  }
  .header-actions {
    gap: 4px;
  }
  .top-nav {
    gap: 0;
  }
  .top-nav a {
    font-size: 13px;
    padding: 6px 10px;
  }
  .page-layout {
    grid-template-columns: 1fr;
  }
  .sidebar {
    display: none;
  }
  .menu-toggle {
    display: inline-flex;
  }
  main {
    padding: 28px 36px 0;
    max-width: 780px;
    width: 100%;
    margin: auto;
  }
  h1 {
    font-size: 42px;
  }
  .lead {
    font-size: 21px;
  }
  .breadcrumb {
    margin-bottom: 21px;
  }
}
@media (max-width: 540px) {
  .header {
    height: auto;
    min-height: 72px;
    padding: 12px 18px;
    flex-wrap: wrap;
    gap: 8px;
  }
  .brand {
    flex: 1;
  }
  .header-actions {
    order: 2;
  }
  .top-nav {
    order: 3;
    width: 100%;
    justify-content: center;
    border-top: 1px solid var(--border);
    padding-top: 10px;
    margin-top: 4px;
    gap: 18px;
  }
  .top-nav a {
    font-size: 14px;
    padding: 5px 16px;
  }
  .brand-caption {
    font-size: 11px;
  }
  .page-layout main {
    padding: 27px 23px 0;
  }
  h1 {
    font-size: 38px;
    letter-spacing: -1.3px;
  }
  h2 {
    font-size: 24px;
  }
  .lead {
    font-size: 20px;
  }
  .intro-box {
    padding: 20px;
    margin-bottom: 34px;
  }
  .intro-box ul {
    font-size: 14px;
  }
  .concept-grid {
    grid-template-columns: 1fr;
  }
  .concept {
    padding: 23px;
  }
  .concept p {
    font-size: 15px;
  }
  .page-footer {
    flex-direction: column;
    gap: 3px;
  }
  .breadcrumb {
    font-size: 12px;
  }
  .heading-link {
    opacity: 1;
    font-size: 16px;
  }
  .progress-note {
    padding: 22px 18px;
  }
  .next-page {
    padding: 20px;
  }
  .learning-path li {
    gap: 14px;
  }
  .learning-path p {
    font-size: 14px;
  }
  html {
    scroll-padding-top: 150px;
  }
  section {
    scroll-margin-top: 155px;
  }
}
@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }
}