:root {
  --paper: #ffffff;
  --paper-2: #fafaf7;
  --paper-3: #f4f3ee;
  --ink: #0b1b2d;
  --ink-mid: #3d4a5c;
  --ink-mute: #6a7585;
  --ink-soft: #98a0aa;
  --accent: #b65d00;
  --accent-2: #d8790e;
  --accent-soft: #fbf0e1;
  --blue: #2e5c8a;
  --blue-soft: #eef3f9;
  --green: #3f6f4a;
  --green-soft: #eef4ef;
  --red: #8a3838;
  --red-soft: #f7ecec;
  --violet: #5b4794;
  --violet-soft: #f1eef7;
  --rule: #e2e0d9;
  --rule-strong: #c9c6bc;
  --font-body: "Public Sans", -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  --font-display: "Iowan Old Style", "Baskerville", "Songti SC", "STSong", "Noto Serif CJK SC", Georgia, serif;
  --font-mono: "JetBrains Mono", "SFMono-Regular", Menlo, Consolas, monospace;
  --max: 1450px;
  --reading: 760px;
  --header-h: 72px;
  --shadow: 0 16px 38px rgba(11, 27, 45, 0.08);
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
  scroll-padding-top: 96px;
}

body {
  margin: 0;
  color: var(--ink);
  background: var(--paper);
  font-family: var(--font-body);
  font-size: 16px;
  line-height: 1.72;
  text-rendering: optimizeLegibility;
}

body.menu-open {
  overflow: hidden;
}

::selection {
  color: var(--ink);
  background: #f2d6b0;
}

a {
  color: inherit;
  text-decoration-thickness: 1px;
  text-underline-offset: 0.22em;
}

a:hover {
  color: var(--accent);
}

button,
input,
select,
textarea {
  color: inherit;
  font: inherit;
}

button,
a {
  -webkit-tap-highlight-color: transparent;
}

:focus-visible {
  outline: 3px solid rgba(182, 93, 0, 0.34);
  outline-offset: 3px;
}

img,
svg {
  max-width: 100%;
}

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

.skip-link {
  position: fixed;
  z-index: 999;
  top: 8px;
  left: 8px;
  padding: 9px 14px;
  color: #fff;
  background: var(--ink);
  transform: translateY(-150%);
}

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

.site-header {
  position: sticky;
  z-index: 100;
  top: 0;
  height: var(--header-h);
  border-bottom: 1px solid var(--rule);
  background: rgba(255, 255, 255, 0.96);
  backdrop-filter: blur(14px);
}

.header-inner {
  display: flex;
  width: min(var(--max), calc(100% - 64px));
  height: 100%;
  margin: 0 auto;
  align-items: center;
  justify-content: space-between;
  gap: 32px;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 13px;
  text-decoration: none;
}

.brand-mark {
  position: relative;
  width: 19px;
  height: 19px;
}

.brand-mark::before,
.brand-mark::after {
  position: absolute;
  content: "";
}

.brand-mark::before {
  inset: 2px;
  border: 1px solid var(--ink);
  transform: rotate(45deg);
}

.brand-mark::after {
  top: 7px;
  left: 7px;
  width: 5px;
  height: 5px;
  border-radius: 50%;
  background: var(--accent);
}

.brand-name {
  font-family: var(--font-display);
  font-size: 22px;
  font-weight: 600;
  letter-spacing: 0.04em;
}

.brand-note {
  padding-left: 13px;
  border-left: 1px solid var(--rule-strong);
  color: var(--ink-mute);
  font-family: var(--font-mono);
  font-size: 9px;
  letter-spacing: 0.16em;
  text-transform: uppercase;
}

.site-nav {
  display: flex;
  align-items: center;
  gap: 30px;
}

.site-nav a {
  position: relative;
  color: var(--ink-mid);
  font-size: 14px;
  font-weight: 650;
  text-decoration: none;
}

.site-nav a::after {
  position: absolute;
  right: 0;
  bottom: -9px;
  left: 0;
  height: 1px;
  content: "";
  background: var(--accent);
  transform: scaleX(0);
  transform-origin: left;
  transition: transform 180ms ease;
}

.site-nav a:hover::after,
.site-nav a[aria-current="page"]::after {
  transform: scaleX(1);
}

.site-nav a[aria-current="page"] {
  color: var(--ink);
}

.menu-toggle {
  display: none;
  width: 42px;
  height: 42px;
  padding: 0;
  border: 1px solid var(--rule-strong);
  background: transparent;
  cursor: pointer;
}

.menu-toggle span,
.menu-toggle::before,
.menu-toggle::after {
  display: block;
  width: 18px;
  height: 1px;
  margin: 5px auto;
  content: "";
  background: var(--ink);
}

.page-shell {
  width: min(var(--max), calc(100% - 64px));
  margin: 0 auto;
}

.hero {
  display: grid;
  min-height: 560px;
  padding: 72px 0 56px;
  align-items: center;
  grid-template-columns: minmax(0, 1.02fr) minmax(460px, 0.98fr);
  gap: 66px;
}

.hero h1 {
  max-width: 680px;
  margin: 0 0 31px;
  font-family: var(--font-display);
  font-size: clamp(54px, 6.1vw, 88px);
  font-weight: 500;
  letter-spacing: -0.045em;
  line-height: 1.04;
}

.hero h1 span {
  display: block;
  color: var(--accent);
  font-style: italic;
}

.hero-copy {
  max-width: 590px;
  margin: 0 0 33px;
  color: var(--ink-mid);
  font-size: 18px;
  line-height: 1.8;
}

.hero-actions {
  display: flex;
  align-items: center;
  gap: 24px;
}

.button-primary,
.button-secondary {
  display: inline-flex;
  min-height: 48px;
  padding: 0 23px;
  align-items: center;
  justify-content: center;
  gap: 10px;
  border: 1px solid var(--accent);
  font-size: 14px;
  font-weight: 750;
  letter-spacing: 0.03em;
  text-decoration: none;
  transition: color 180ms ease, background 180ms ease, transform 180ms ease;
}

.button-primary {
  color: #fff;
  background: var(--accent);
}

.button-primary:hover {
  color: #fff;
  background: #914900;
  transform: translateY(-2px);
}

.button-secondary {
  padding-right: 5px;
  padding-left: 5px;
  border-color: transparent;
  border-bottom-color: var(--ink);
  color: var(--ink);
}

.button-secondary:hover {
  color: var(--accent);
  border-bottom-color: var(--accent);
}

.arrow-icon {
  display: inline-block;
  width: 22px;
  height: 10px;
}

.hero-visual {
  position: relative;
  min-height: 445px;
}

.hero-visual::before {
  position: absolute;
  z-index: -1;
  inset: 0;
  content: "";
  opacity: 0.33;
  background-image: linear-gradient(var(--rule) 1px, transparent 1px), linear-gradient(90deg, var(--rule) 1px, transparent 1px);
  background-size: 32px 32px;
  mask-image: linear-gradient(to right, transparent, #000 18%, #000 82%, transparent);
}

.hero-diagram {
  width: 100%;
  height: auto;
  overflow: visible;
}

.diagram-flow {
  stroke-dasharray: 5 7;
  animation: dash 9s linear infinite;
}

@keyframes dash {
  to { stroke-dashoffset: -72; }
}

.stats-band {
  display: grid;
  padding: 29px 0 31px;
  border-top: 1px solid var(--ink);
  border-bottom: 1px solid var(--rule-strong);
  grid-template-columns: repeat(4, 1fr);
}

.stat {
  min-height: 103px;
  padding: 0 28px;
  border-left: 1px solid var(--rule);
}

.stat:first-child {
  padding-left: 0;
  border-left: 0;
}

.stat-value {
  display: block;
  margin-bottom: 6px;
  font-family: var(--font-display);
  font-size: 53px;
  font-weight: 400;
  letter-spacing: -0.04em;
  line-height: 1;
}

.stat-label {
  color: var(--ink-mid);
  font-size: 13px;
}

.stat-label small {
  display: block;
  margin-top: 3px;
  color: var(--ink-mute);
  font-family: var(--font-mono);
  font-size: 9px;
  letter-spacing: 0.17em;
  text-transform: uppercase;
}

.quick-jump {
  display: flex;
  padding: 21px 0;
  align-items: center;
  gap: 26px;
  border-bottom: 1px solid var(--ink);
  overflow-x: auto;
  scrollbar-width: thin;
}

.quick-jump-label {
  color: var(--ink-mute);
  font-family: var(--font-mono);
  font-size: 9px;
  letter-spacing: 0.17em;
  white-space: nowrap;
}

.quick-jump a {
  color: var(--ink-mid);
  font-size: 13px;
  font-weight: 650;
  text-decoration: none;
  white-space: nowrap;
}

.quick-jump a span {
  margin-right: 5px;
  color: var(--accent);
  font-family: var(--font-display);
  font-style: italic;
}

.section-heading {
  display: grid;
  margin: 0 0 48px;
  align-items: end;
  grid-template-columns: minmax(0, 1fr) minmax(300px, 0.55fr);
  gap: 40px;
}

.section-heading h2,
.page-intro h1 {
  margin: 0;
  font-family: var(--font-display);
  font-size: clamp(43px, 5vw, 70px);
  font-weight: 500;
  letter-spacing: -0.035em;
  line-height: 1.08;
}

.section-heading p,
.page-intro > p {
  margin: 0;
  color: var(--ink-mid);
  line-height: 1.78;
}

.learning-map-section {
  padding: 112px 0 90px;
}

.stage-map {
  position: relative;
  border-top: 1px solid var(--ink);
}

.stage-row {
  display: grid;
  min-height: 242px;
  padding: 34px 0;
  align-items: start;
  border-bottom: 1px solid var(--rule-strong);
  grid-template-columns: 132px minmax(220px, 0.7fr) minmax(0, 1.6fr);
  gap: 34px;
}

.stage-number {
  color: var(--accent);
  font-family: var(--font-display);
  font-size: 73px;
  font-style: italic;
  font-weight: 400;
  line-height: 0.9;
}

.stage-meta {
  padding-right: 28px;
  border-right: 1px solid var(--rule);
}

.stage-meta .mono-label,
.stage-time,
.chapter-kicker,
.block-label,
.eyeline,
.toc-label {
  color: var(--ink-mute);
  font-family: var(--font-mono);
  font-size: 9px;
  font-weight: 650;
  letter-spacing: 0.16em;
  text-transform: uppercase;
}

.stage-meta h3 {
  margin: 12px 0 12px;
  font-family: var(--font-display);
  font-size: 29px;
  font-weight: 520;
  line-height: 1.22;
}

.stage-meta p {
  margin: 0 0 15px;
  color: var(--ink-mid);
  font-size: 14px;
  line-height: 1.68;
}

.stage-output {
  display: inline-flex;
  padding: 5px 8px;
  border: 1px solid var(--rule-strong);
  background: var(--paper-2);
  color: var(--ink-mid);
  font-family: var(--font-mono);
  font-size: 10px;
}

.chapter-list {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0 26px;
}

.chapter-list a {
  display: grid;
  padding: 12px 0;
  align-items: baseline;
  border-bottom: 1px dotted var(--rule-strong);
  grid-template-columns: 42px minmax(0, 1fr) 24px;
  gap: 8px;
  text-decoration: none;
}

.chapter-list a:hover .chapter-name {
  color: var(--accent);
}

.chapter-index {
  color: var(--ink-soft);
  font-family: var(--font-mono);
  font-size: 10px;
}

.chapter-name {
  color: var(--ink-mid);
  font-size: 14px;
  line-height: 1.45;
}

.chapter-check {
  position: relative;
  width: 16px;
  height: 16px;
  border: 1px solid var(--rule-strong);
}

.chapter-check.is-complete {
  border-color: var(--green);
  background: var(--green);
}

.chapter-check.is-complete::after {
  position: absolute;
  top: 1px;
  left: 4px;
  width: 4px;
  height: 8px;
  content: "";
  border: solid #fff;
  border-width: 0 2px 2px 0;
  transform: rotate(45deg);
}

.site-footer {
  margin-top: 110px;
  padding: 48px 0 54px;
  border-top: 1px solid var(--ink);
  background: var(--paper-2);
}

.footer-inner {
  display: grid;
  width: min(var(--max), calc(100% - 64px));
  margin: 0 auto;
  grid-template-columns: 1fr auto;
  gap: 40px;
}

.footer-title {
  margin: 0 0 8px;
  font-family: var(--font-display);
  font-size: 27px;
}

.footer-copy {
  max-width: 610px;
  margin: 0;
  color: var(--ink-mute);
  font-size: 13px;
}

.footer-links {
  display: flex;
  align-items: start;
  gap: 24px;
  font-size: 13px;
}

.page-intro {
  display: grid;
  padding: 92px 0 64px;
  border-bottom: 1px solid var(--ink);
  grid-template-columns: minmax(0, 1.2fr) minmax(320px, 0.55fr);
  gap: 60px;
}

.page-intro .eyeline {
  display: block;
  margin-bottom: 18px;
  color: var(--accent);
}

.page-intro h1 {
  max-width: 820px;
}

.page-intro > p {
  align-self: end;
}

.roadmap-grid {
  padding-top: 68px;
}

.roadmap-stage {
  display: grid;
  padding: 35px 0 42px;
  border-bottom: 1px solid var(--rule-strong);
  grid-template-columns: 95px minmax(220px, 0.65fr) minmax(0, 1.35fr);
  gap: 30px;
}

.roadmap-stage .stage-number {
  font-size: 58px;
}

.roadmap-stage h2 {
  margin: 0 0 8px;
  font-family: var(--font-display);
  font-size: 31px;
  font-weight: 520;
}

.roadmap-stage p {
  margin: 0;
  color: var(--ink-mid);
  font-size: 14px;
}

.roadmap-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 14px;
}

.roadmap-table th,
.roadmap-table td {
  padding: 10px 8px;
  border-bottom: 1px dotted var(--rule-strong);
  text-align: left;
  vertical-align: top;
}

.roadmap-table th {
  width: 116px;
  color: var(--ink-mute);
  font-family: var(--font-mono);
  font-size: 9px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.bridge-band {
  display: grid;
  margin: 34px 0;
  padding: 24px 26px;
  border-left: 3px solid var(--accent);
  background: var(--accent-soft);
  grid-template-columns: 150px 1fr;
  gap: 22px;
}

.bridge-band h3 {
  margin: 0;
  font-family: var(--font-display);
  font-size: 22px;
  font-weight: 550;
}

.bridge-band p {
  margin: 0;
  color: var(--ink-mid);
  font-size: 14px;
}

.lesson-progress-bar {
  position: fixed;
  z-index: 120;
  top: 0;
  left: 0;
  width: 0;
  height: 3px;
  background: var(--accent);
  transition: width 80ms linear;
}

.lesson-shell {
  display: grid;
  width: min(1460px, calc(100% - 48px));
  margin: 0 auto;
  padding: 42px 0 0;
  align-items: start;
  grid-template-columns: 220px minmax(0, var(--reading)) 210px;
  justify-content: center;
  gap: 48px;
}

.lesson-toc,
.lesson-aside {
  position: sticky;
  top: calc(var(--header-h) + 30px);
  max-height: calc(100vh - var(--header-h) - 60px);
  overflow-y: auto;
  scrollbar-width: thin;
}

.lesson-toc {
  padding-right: 22px;
  border-right: 1px solid var(--rule);
}

.lesson-toc ol {
  margin: 13px 0 0;
  padding: 0;
  list-style: none;
}

.lesson-toc a {
  display: block;
  padding: 7px 0 7px 14px;
  border-left: 1px solid var(--rule-strong);
  color: var(--ink-mute);
  font-size: 12px;
  line-height: 1.45;
  text-decoration: none;
}

.lesson-toc a:hover,
.lesson-toc a.is-active {
  border-left-color: var(--accent);
  color: var(--ink);
}

.lesson-aside {
  padding-left: 18px;
  border-left: 1px solid var(--rule);
}

.aside-progress {
  margin-bottom: 30px;
}

.aside-progress strong {
  display: block;
  margin: 8px 0 12px;
  font-family: var(--font-display);
  font-size: 31px;
  font-weight: 500;
}

.progress-track {
  height: 3px;
  background: var(--rule);
}

.progress-track span {
  display: block;
  width: 0;
  height: 100%;
  background: var(--accent);
}

.aside-note {
  padding: 18px 0;
  border-top: 1px solid var(--rule-strong);
}

.aside-note h3 {
  margin: 0 0 8px;
  font-family: var(--font-display);
  font-size: 20px;
  font-weight: 550;
}

.aside-note p {
  margin: 0;
  color: var(--ink-mid);
  font-size: 12px;
  line-height: 1.7;
}

.lesson-main {
  min-width: 0;
}

.breadcrumb {
  display: flex;
  margin-bottom: 34px;
  align-items: center;
  gap: 9px;
  color: var(--ink-mute);
  font-family: var(--font-mono);
  font-size: 9px;
  letter-spacing: 0.09em;
  text-transform: uppercase;
}

.breadcrumb a {
  text-decoration: none;
}

.chapter-header {
  padding-bottom: 39px;
  border-bottom: 1px solid var(--ink);
}

.chapter-header h1 {
  margin: 0 0 25px;
  font-family: var(--font-display);
  font-size: clamp(48px, 5.8vw, 76px);
  font-weight: 500;
  letter-spacing: -0.04em;
  line-height: 1.09;
}

.chapter-meta {
  display: flex;
  padding: 12px 0;
  align-items: center;
  gap: 14px;
  border-top: 1px solid var(--rule);
  border-bottom: 1px solid var(--rule);
  color: var(--ink-mid);
  font-family: var(--font-mono);
  font-size: 10px;
  letter-spacing: 0.08em;
}

.chapter-meta .meta-accent {
  color: var(--accent);
}

.chapter-opening {
  margin: 50px 0 55px;
  font-family: var(--font-display);
  font-size: 26px;
  line-height: 1.65;
}

.chapter-opening p {
  margin: 0;
}

.learning-objectives {
  margin: 40px 0 54px;
  padding: 23px 26px;
  border-left: 3px solid var(--accent);
  background: var(--paper-2);
}

.learning-objectives h2 {
  margin: 0 0 12px;
  font-family: var(--font-display);
  font-size: 24px;
  font-weight: 560;
}

.learning-objectives ul {
  margin: 0;
  padding-left: 20px;
}

.anchor-grid {
  display: grid;
  margin: 0 0 68px;
  border-top: 1px solid var(--ink);
  grid-template-columns: repeat(3, minmax(0, 1fr));
}

.anchor-card {
  min-height: 190px;
  padding: 23px 20px 23px 0;
  border-right: 1px solid var(--rule);
}

.anchor-card + .anchor-card {
  padding-left: 20px;
}

.anchor-card:last-child {
  border-right: 0;
}

.anchor-card .anchor-number {
  color: var(--accent);
  font-family: var(--font-display);
  font-size: 34px;
  font-style: italic;
}

.anchor-card h3 {
  margin: 12px 0 7px;
  font-family: var(--font-display);
  font-size: 21px;
  font-weight: 560;
}

.anchor-card p {
  margin: 0;
  color: var(--ink-mid);
  font-size: 13px;
  line-height: 1.65;
}

.lesson-section {
  margin: 0 0 78px;
}

.lesson-section > h2 {
  display: flex;
  margin: 0 0 27px;
  padding-bottom: 14px;
  align-items: baseline;
  border-bottom: 1px solid var(--rule-strong);
  font-family: var(--font-display);
  font-size: 38px;
  font-weight: 520;
  letter-spacing: -0.025em;
  line-height: 1.2;
}

.lesson-section > h2::before {
  width: 28px;
  height: 1px;
  margin-right: 12px;
  content: "";
  background: var(--accent);
}

.lesson-section h3 {
  margin: 35px 0 12px;
  font-family: var(--font-display);
  font-size: 26px;
  font-weight: 560;
}

.lesson-section p {
  margin: 0 0 18px;
}

.lesson-section ul,
.lesson-section ol {
  margin: 16px 0 24px;
  padding-left: 25px;
}

.lesson-section li {
  margin-bottom: 7px;
}

.formula {
  display: block;
  margin: 25px 0;
  padding: 22px 24px;
  border-top: 1px solid var(--rule-strong);
  border-bottom: 1px solid var(--rule-strong);
  background: var(--paper-2);
  font-family: var(--font-display);
  font-size: 22px;
  font-style: italic;
  text-align: center;
  overflow-x: auto;
}

code {
  padding: 0.12em 0.32em;
  color: #264f77;
  background: var(--blue-soft);
  font-family: var(--font-mono);
  font-size: 0.88em;
}

pre {
  position: relative;
  margin: 24px 0;
  padding: 24px;
  border: 1px solid #1d3045;
  background: #0f2032;
  color: #e7edf3;
  font-family: var(--font-mono);
  font-size: 13px;
  line-height: 1.65;
  overflow-x: auto;
}

pre code {
  padding: 0;
  color: inherit;
  background: transparent;
  font-size: inherit;
}

.copy-code {
  position: absolute;
  top: 10px;
  right: 10px;
  padding: 5px 8px;
  border: 1px solid rgba(255, 255, 255, 0.35);
  color: #fff;
  background: rgba(255, 255, 255, 0.07);
  font-family: var(--font-mono);
  font-size: 9px;
  letter-spacing: 0.1em;
  cursor: pointer;
}

.worked-example,
.concept-block,
.warning-block,
.debug-block {
  margin: 29px 0;
  padding: 24px 27px;
  border-left: 3px solid var(--blue);
  background: var(--blue-soft);
}

.worked-example {
  border-left-color: var(--accent);
  background: var(--accent-soft);
}

.warning-block {
  border-left-color: var(--red);
  background: var(--red-soft);
}

.debug-block {
  border-left-color: var(--green);
  background: var(--green-soft);
}

.worked-example > :last-child,
.concept-block > :last-child,
.warning-block > :last-child,
.debug-block > :last-child {
  margin-bottom: 0;
}

.worked-example .block-label,
.concept-block .block-label,
.warning-block .block-label,
.debug-block .block-label {
  display: block;
  margin-bottom: 10px;
  color: currentColor;
}

.teaching-figure {
  margin: 38px 0 42px;
}

.teaching-figure-frame {
  padding: 14px;
  border-top: 1px solid var(--ink);
  border-bottom: 1px solid var(--rule-strong);
  background: var(--paper);
}

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

.teaching-figure figcaption {
  margin-top: 12px;
  color: var(--ink-mute);
  font-size: 12px;
  line-height: 1.65;
}

.check-yourself {
  margin: 33px 0;
  padding: 23px 26px;
  border: 1px solid var(--rule-strong);
}

.check-yourself summary,
.answer-reveal summary {
  color: var(--ink);
  font-weight: 750;
  cursor: pointer;
}

.check-yourself[open] summary,
.answer-reveal[open] summary {
  margin-bottom: 13px;
}

.misconceptions,
.practice-section,
.mastery-section,
.stuck-section {
  margin: 76px 0;
  padding-top: 35px;
  border-top: 1px solid var(--ink);
}

.misconceptions > h2,
.practice-section > h2,
.mastery-section > h2,
.stuck-section > h2 {
  margin: 0 0 26px;
  font-family: var(--font-display);
  font-size: 38px;
  font-weight: 520;
}

.misconception-list {
  border-top: 1px solid var(--rule);
}

.misconception-item {
  display: grid;
  padding: 21px 0;
  border-bottom: 1px solid var(--rule);
  grid-template-columns: 220px 1fr;
  gap: 28px;
}

.misconception-item h3 {
  margin: 0;
  font-family: var(--font-display);
  font-size: 20px;
  font-weight: 560;
}

.misconception-item p {
  margin: 0;
  color: var(--ink-mid);
}

.stuck-steps {
  counter-reset: stuck;
  margin: 0;
  padding: 0;
  list-style: none;
}

.stuck-steps li {
  display: grid;
  padding: 14px 0;
  border-bottom: 1px dotted var(--rule-strong);
  grid-template-columns: 42px 1fr;
  gap: 12px;
}

.stuck-steps li::before {
  color: var(--accent);
  content: "0" counter(stuck);
  counter-increment: stuck;
  font-family: var(--font-display);
  font-size: 22px;
  font-style: italic;
}

.practice-list {
  display: grid;
  gap: 26px;
}

.practice-card {
  border-top: 1px solid var(--rule-strong);
  border-bottom: 1px solid var(--rule-strong);
  background: var(--paper-2);
}

.practice-head {
  display: grid;
  padding: 21px 24px;
  align-items: baseline;
  grid-template-columns: 62px 1fr;
  gap: 14px;
  background: var(--paper-3);
}

.practice-number {
  color: var(--accent);
  font-family: var(--font-display);
  font-size: 31px;
  font-style: italic;
}

.practice-head h3 {
  margin: 0;
  font-family: var(--font-display);
  font-size: 24px;
  font-weight: 550;
}

.practice-body {
  display: grid;
  padding: 23px 24px;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 18px 30px;
}

.practice-field strong {
  display: block;
  margin-bottom: 4px;
  color: var(--ink-mute);
  font-family: var(--font-mono);
  font-size: 9px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.practice-field p {
  margin: 0;
  color: var(--ink-mid);
  font-size: 14px;
}

.answer-reveal {
  grid-column: 1 / -1;
  padding: 14px 0 0;
  border-top: 1px dotted var(--rule-strong);
}

.answer-reveal p {
  margin: 8px 0 0;
}

.mastery-section {
  padding: 35px 31px 31px;
  border: 1px solid var(--ink);
  background: var(--paper);
}

.mastery-section > h2 {
  margin-top: 0;
}

.chapter-summary {
  margin: 76px 0 36px;
  padding: 34px 0;
  border-top: 1px solid var(--ink);
  border-bottom: 1px solid var(--ink);
}

.chapter-summary h2 {
  margin: 0 0 18px;
  font-family: var(--font-display);
  font-size: 34px;
  font-weight: 520;
}

.chapter-summary ul {
  margin: 0;
  padding-left: 21px;
}

.completion-control {
  display: flex;
  margin: 37px 0;
  padding: 22px 0;
  align-items: center;
  justify-content: space-between;
  gap: 20px;
}

.complete-button {
  min-height: 44px;
  padding: 0 18px;
  border: 1px solid var(--green);
  color: var(--green);
  background: transparent;
  font-weight: 750;
  cursor: pointer;
}

.complete-button.is-complete {
  color: #fff;
  background: var(--green);
}

.chapter-navigation {
  display: grid;
  margin-top: 45px;
  border-top: 1px solid var(--rule-strong);
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.chapter-navigation a {
  min-height: 116px;
  padding: 24px 0;
  text-decoration: none;
}

.chapter-navigation a + a {
  padding-left: 28px;
  border-left: 1px solid var(--rule);
  text-align: right;
}

.chapter-navigation small {
  display: block;
  margin-bottom: 7px;
  color: var(--ink-mute);
  font-family: var(--font-mono);
  font-size: 9px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.chapter-navigation strong {
  font-family: var(--font-display);
  font-size: 19px;
  font-weight: 550;
}

.paper-track {
  padding-top: 62px;
}

.paper-item {
  display: grid;
  padding: 40px 0 48px;
  border-bottom: 1px solid var(--rule-strong);
  grid-template-columns: 130px minmax(260px, 0.65fr) minmax(0, 1.35fr);
  gap: 34px;
}

.paper-index {
  color: var(--accent);
  font-family: var(--font-display);
  font-size: 60px;
  font-style: italic;
  line-height: 1;
}

.paper-meta h2 {
  margin: 6px 0 12px;
  font-family: var(--font-display);
  font-size: 29px;
  font-weight: 540;
  line-height: 1.28;
}

.paper-meta p {
  margin: 0 0 12px;
  color: var(--ink-mid);
  font-size: 14px;
}

.paper-link {
  color: var(--accent);
  font-size: 13px;
  font-weight: 750;
}

.paper-guide {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 17px 25px;
}

.paper-guide section {
  padding-top: 10px;
  border-top: 1px dotted var(--rule-strong);
}

.paper-guide h3 {
  margin: 0 0 5px;
  color: var(--ink-mute);
  font-family: var(--font-mono);
  font-size: 9px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.paper-guide p,
.paper-guide ul {
  margin: 0;
  color: var(--ink-mid);
  font-size: 13px;
}

.paper-guide ul {
  padding-left: 18px;
}

.project-hero {
  display: grid;
  margin: 64px 0 0;
  padding: 40px 0 56px;
  border-bottom: 1px solid var(--ink);
  grid-template-columns: 0.82fr 1.18fr;
  gap: 60px;
}

.project-hero h2 {
  margin: 0;
  font-family: var(--font-display);
  font-size: 46px;
  font-weight: 500;
  line-height: 1.12;
}

.project-hero p {
  margin: 0;
  color: var(--ink-mid);
  font-size: 18px;
}

.project-tracks {
  display: grid;
  margin: 48px 0 68px;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  border-top: 1px solid var(--ink);
  border-bottom: 1px solid var(--rule-strong);
}

.project-track {
  min-height: 270px;
  padding: 28px 27px;
  border-right: 1px solid var(--rule);
}

.project-track:last-child {
  border-right: 0;
}

.project-track h3 {
  margin: 18px 0 11px;
  font-family: var(--font-display);
  font-size: 28px;
  font-weight: 550;
}

.project-track p {
  margin: 0 0 18px;
  color: var(--ink-mid);
  font-size: 14px;
}

.project-checklist {
  display: grid;
  margin: 32px 0 66px;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 0 36px;
}

.project-check {
  display: grid;
  padding: 15px 0;
  border-bottom: 1px dotted var(--rule-strong);
  grid-template-columns: 26px 1fr;
  gap: 12px;
}

.project-check::before {
  width: 15px;
  height: 15px;
  margin-top: 5px;
  border: 1px solid var(--green);
  content: "";
}

.rubric-table {
  width: 100%;
  margin: 27px 0 66px;
  border-collapse: collapse;
}

.rubric-table th,
.rubric-table td {
  padding: 15px 14px;
  border-top: 1px solid var(--rule-strong);
  text-align: left;
}

.rubric-table th {
  color: var(--ink-mute);
  font-family: var(--font-mono);
  font-size: 9px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.rubric-table td:last-child {
  font-family: var(--font-display);
  font-size: 25px;
  text-align: right;
}

.glossary-tools {
  position: sticky;
  z-index: 20;
  top: var(--header-h);
  display: flex;
  padding: 20px 0;
  border-bottom: 1px solid var(--rule-strong);
  background: rgba(255, 255, 255, 0.96);
  align-items: center;
  gap: 20px;
}

.glossary-search {
  flex: 1;
  height: 48px;
  padding: 0 16px;
  border: 1px solid var(--rule-strong);
  border-radius: 0;
  background: var(--paper);
}

.glossary-count {
  color: var(--ink-mute);
  font-family: var(--font-mono);
  font-size: 10px;
  white-space: nowrap;
}

.glossary-list {
  margin-top: 32px;
  border-top: 1px solid var(--ink);
}

.glossary-item {
  display: grid;
  padding: 28px 0 31px;
  border-bottom: 1px solid var(--rule-strong);
  grid-template-columns: 0.66fr 1.34fr;
  gap: 44px;
}

.glossary-item[hidden] {
  display: none;
}

.glossary-item h2 {
  margin: 0 0 5px;
  font-family: var(--font-display);
  font-size: 29px;
  font-weight: 550;
}

.glossary-en {
  color: var(--accent);
  font-family: var(--font-mono);
  font-size: 10px;
  letter-spacing: 0.08em;
}

.glossary-body p {
  margin: 0 0 10px;
  color: var(--ink-mid);
}

.glossary-links {
  color: var(--ink-mute);
  font-size: 12px;
}

.callout-band {
  margin: 68px 0;
  padding: 38px 42px;
  border-top: 1px solid var(--ink);
  border-bottom: 1px solid var(--ink);
  background: var(--paper-2);
}

.callout-band h2 {
  margin: 0 0 14px;
  font-family: var(--font-display);
  font-size: 36px;
  font-weight: 520;
}

.callout-band p {
  max-width: 850px;
  margin: 0;
  color: var(--ink-mid);
}

.empty-state {
  padding: 48px 0;
  color: var(--ink-mute);
  text-align: center;
}

.reveal {
  opacity: 0;
  transform: translateY(18px);
  transition: opacity 560ms ease, transform 560ms ease;
}

.reveal.is-visible {
  opacity: 1;
  transform: translateY(0);
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { animation-duration: 0.01ms !important; animation-iteration-count: 1 !important; transition-duration: 0.01ms !important; }
  .reveal { opacity: 1; transform: none; }
}

@media (max-width: 1180px) {
  .hero {
    grid-template-columns: minmax(0, 0.95fr) minmax(420px, 1.05fr);
    gap: 35px;
  }

  .lesson-shell {
    grid-template-columns: 205px minmax(0, var(--reading));
    gap: 36px;
  }

  .lesson-aside {
    display: none;
  }
}

@media (max-width: 960px) {
  :root { --header-h: 64px; }

  .header-inner,
  .page-shell,
  .footer-inner {
    width: min(100% - 40px, var(--max));
  }

  .brand-note { display: none; }

  .site-nav {
    position: fixed;
    z-index: 99;
    inset: var(--header-h) 0 auto;
    display: none;
    padding: 25px 20px 30px;
    border-bottom: 1px solid var(--ink);
    background: var(--paper);
    flex-direction: column;
    align-items: stretch;
    gap: 0;
  }

  .site-nav.is-open { display: flex; }

  .site-nav a {
    padding: 13px 0;
    border-bottom: 1px solid var(--rule);
  }

  .site-nav a::after { display: none; }

  .menu-toggle { display: block; }

  .hero {
    min-height: auto;
    padding: 68px 0 55px;
    grid-template-columns: 1fr;
  }

  .hero-copy { max-width: 690px; }

  .hero-visual {
    max-width: 690px;
    min-height: 0;
    margin: 0 auto;
  }

  .section-heading,
  .page-intro {
    grid-template-columns: 1fr;
    gap: 25px;
  }

  .stage-row,
  .roadmap-stage {
    grid-template-columns: 92px minmax(210px, 0.58fr) minmax(0, 1.42fr);
    gap: 22px;
  }

  .stage-number { font-size: 58px; }

  .chapter-list { grid-template-columns: 1fr; }

  .lesson-shell {
    width: min(100% - 40px, var(--reading));
    grid-template-columns: 1fr;
  }

  .lesson-toc {
    position: static;
    max-height: none;
    padding: 0 0 21px;
    border-right: 0;
    border-bottom: 1px solid var(--rule);
  }

  .lesson-toc ol {
    display: flex;
    gap: 8px;
    overflow-x: auto;
  }

  .lesson-toc a {
    min-width: 175px;
    padding: 8px 10px;
    border: 1px solid var(--rule);
  }

  .paper-item {
    grid-template-columns: 90px minmax(0, 1fr);
  }

  .paper-guide {
    grid-column: 2;
  }
}

@media (max-width: 720px) {
  body { font-size: 15px; }

  .header-inner,
  .page-shell,
  .footer-inner,
  .lesson-shell {
    width: min(100% - 28px, var(--max));
  }

  .brand-name { font-size: 19px; }

  .hero { padding-top: 49px; }

  .hero h1 {
    margin-bottom: 24px;
    font-size: clamp(46px, 14vw, 65px);
  }

  .hero-copy { font-size: 16px; }

  .hero-actions { align-items: stretch; flex-direction: column; gap: 12px; }

  .button-primary,
  .button-secondary { width: 100%; }

  .hero-visual { margin-top: 10px; }

  .stats-band { grid-template-columns: repeat(2, 1fr); }

  .stat {
    min-height: 98px;
    padding: 15px 16px;
    border-bottom: 1px solid var(--rule);
  }

  .stat:nth-child(odd) { padding-left: 0; border-left: 0; }
  .stat:nth-child(even) { padding-right: 0; }

  .stat-value { font-size: 43px; }

  .learning-map-section { padding: 76px 0 40px; }

  .section-heading h2,
  .page-intro h1 { font-size: 43px; }

  .stage-row,
  .roadmap-stage {
    padding: 30px 0;
    grid-template-columns: 64px 1fr;
    gap: 18px;
  }

  .stage-number { font-size: 47px; }

  .stage-meta {
    padding-right: 0;
    border-right: 0;
  }

  .chapter-list,
  .roadmap-table,
  .roadmap-stage > :last-child {
    grid-column: 2;
  }

  .stage-row .chapter-list { grid-column: 2; }

  .page-intro { padding: 60px 0 44px; }

  .bridge-band { grid-template-columns: 1fr; }

  .lesson-shell { padding-top: 28px; }

  .chapter-header h1 { font-size: 48px; }

  .chapter-meta { align-items: center; flex-flow: row wrap; gap: 5px 10px; }
  .chapter-meta .meta-separator { display: none; }

  .chapter-opening { margin: 36px 0 40px; font-size: 22px; }

  .anchor-grid { grid-template-columns: 1fr; }

  .anchor-card,
  .anchor-card + .anchor-card {
    min-height: 0;
    padding: 18px 0;
    border-right: 0;
    border-bottom: 1px solid var(--rule);
  }

  .lesson-section > h2,
  .misconceptions > h2,
  .practice-section > h2,
  .mastery-section > h2,
  .stuck-section > h2 { font-size: 31px; }

  .formula { font-size: 19px; }

  pre { margin-right: -14px; margin-left: -14px; padding: 18px 14px; }

  .misconception-item { grid-template-columns: 1fr; gap: 7px; }

  .practice-body { grid-template-columns: 1fr; }
  .answer-reveal { grid-column: 1; }

  .chapter-navigation { grid-template-columns: 1fr; }
  .chapter-navigation a + a { padding-left: 0; border-top: 1px solid var(--rule); border-left: 0; text-align: left; }

  .paper-item { grid-template-columns: 64px 1fr; gap: 18px; }
  .paper-index { font-size: 46px; }
  .paper-guide { grid-column: 1 / -1; grid-template-columns: 1fr; }

  .project-hero { grid-template-columns: 1fr; gap: 22px; }
  .project-tracks { grid-template-columns: 1fr; }
  .project-track { min-height: 0; border-right: 0; border-bottom: 1px solid var(--rule); }
  .project-checklist { grid-template-columns: 1fr; }

  .glossary-item { grid-template-columns: 1fr; gap: 18px; }
  .glossary-tools { align-items: stretch; flex-direction: column; gap: 9px; }

  .footer-inner { grid-template-columns: 1fr; }
  .footer-links { flex-wrap: wrap; }
}