:root {
  --ink: #13294b;
  --ink-soft: #38556d;
  --muted: #5f6f83;
  --paper: #f5f4ee;
  --surface: #fffef9;
  --surface-alt: #eaf2ef;
  --teal: #0f766e;
  --teal-dark: #0b5f59;
  --teal-pale: #d9eeea;
  --blue: #245a8d;
  --blue-pale: #e5eef5;
  --amber: #9a5c09;
  --amber-pale: #fbf0d9;
  --red: #a62c24;
  --red-pale: #fae9e5;
  --border: #d8dfe2;
  --border-strong: #b5c3ca;
  --sans: Inter, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --serif: "Iowan Old Style", "Palatino Linotype", Palatino, Georgia, serif;
  --mono: "Cascadia Code", "SFMono-Regular", Consolas, monospace;
  --sidebar: 286px;
  --topbar: 64px;
  --width: 1140px;
}

* { box-sizing: border-box; }

html {
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--topbar) + 24px);
}

body {
  margin: 0;
  color: var(--ink);
  background: var(--paper);
  font-family: var(--sans);
  font-size: 16px;
  line-height: 1.68;
}

a {
  color: var(--teal);
  text-decoration-thickness: 1px;
  text-underline-offset: 0.2em;
}

a:hover { color: var(--teal-dark); }

a:focus-visible,
button:focus-visible,
summary:focus-visible {
  outline: 3px solid var(--amber);
  outline-offset: 3px;
}

code,
pre {
  font-family: var(--mono);
}

.skip-link {
  position: fixed;
  top: 10px;
  left: 12px;
  z-index: 1000;
  padding: 10px 14px;
  color: white;
  background: var(--ink);
  border-radius: 6px;
  transform: translateY(-160%);
}

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

.reading-progress {
  position: fixed;
  inset: 0 0 auto;
  z-index: 110;
  height: 3px;
}

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

.topbar {
  position: fixed;
  inset: 0 0 auto;
  z-index: 100;
  height: var(--topbar);
  display: grid;
  grid-template-columns: auto 1fr auto;
  gap: 18px;
  align-items: center;
  padding: 0 26px;
  background: rgba(255, 254, 249, 0.96);
  border-bottom: 1px solid var(--border);
  backdrop-filter: blur(12px);
}

.menu-button {
  display: none;
  width: 44px;
  height: 44px;
  padding: 0;
  color: var(--ink);
  background: transparent;
  border: 1px solid var(--border);
  border-radius: 50%;
  cursor: pointer;
}

.topbar-title {
  color: var(--ink);
  font-family: var(--serif);
  font-size: 1.05rem;
  font-weight: 700;
  text-decoration: none;
}

.topbar-meta {
  display: flex;
  gap: 18px;
  align-items: center;
  color: var(--muted);
  font-size: 0.72rem;
  font-weight: 800;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.topbar-meta a {
  display: inline-flex;
  min-height: 44px;
  align-items: center;
  color: var(--ink);
  text-decoration: none;
}

.site-shell {
  display: grid;
  grid-template-columns: var(--sidebar) minmax(0, 1fr);
  min-height: 100vh;
  padding-top: var(--topbar);
}

.sidebar {
  position: sticky;
  top: var(--topbar);
  height: calc(100vh - var(--topbar));
  display: flex;
  flex-direction: column;
  overflow-y: auto;
  padding: 26px 22px 22px;
  background: #efeee7;
  border-right: 1px solid var(--border);
}

.brand {
  display: flex;
  gap: 12px;
  align-items: center;
  padding-bottom: 22px;
  border-bottom: 1px solid var(--border);
}

.brand svg {
  flex: 0 0 auto;
  color: var(--teal);
}

.brand-kicker,
.brand-title,
.nav-label,
.eyebrow,
.mini-label,
.fig-label {
  margin: 0;
  font-size: 0.67rem;
  font-weight: 800;
  letter-spacing: 0.12em;
  line-height: 1.4;
  text-transform: uppercase;
}

.brand-kicker {
  color: var(--muted);
}

.brand-title {
  margin-top: 3px;
  color: var(--ink);
  font-size: 0.82rem;
  letter-spacing: 0.03em;
  text-transform: none;
}

.course-links {
  display: flex;
  flex-direction: column;
  gap: 3px;
  padding-top: 23px;
}

.nav-label {
  padding: 0 10px 8px;
  color: #5c6b7d;
}

.nav-link {
  display: grid;
  grid-template-columns: 27px 1fr;
  gap: 3px;
  min-height: 42px;
  align-items: center;
  padding: 6px 10px;
  color: var(--ink-soft);
  border-radius: 5px;
  font-size: 0.82rem;
  line-height: 1.35;
  text-decoration: none;
}

.nav-link span {
  color: #657588;
  font-family: var(--mono);
  font-size: 0.68rem;
}

.nav-link:hover {
  color: var(--ink);
  background: rgba(255, 254, 249, 0.7);
}

.nav-link.is-active {
  color: var(--ink);
  background: var(--surface);
  box-shadow: inset 3px 0 var(--teal);
}

.sidebar-note {
  margin-top: auto;
  padding: 14px;
  color: var(--muted);
  background: rgba(255, 254, 249, 0.64);
  border: 1px solid var(--border);
  font-size: 0.74rem;
  line-height: 1.55;
}

.mobile-scrim {
  position: fixed;
  inset: var(--topbar) 0 0;
  z-index: 70;
  background: rgba(15, 31, 44, 0.38);
}

main { min-width: 0; }

.chapter {
  width: min(100%, var(--width));
  margin: 0 auto;
  padding: 82px 54px;
  border-bottom: 1px solid var(--border);
}

.hero {
  display: grid;
  grid-template-columns: minmax(0, 1.08fr) minmax(360px, 0.92fr);
  gap: 44px;
  align-items: center;
  min-height: calc(100vh - var(--topbar));
}

.eyebrow {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  align-items: center;
  color: var(--teal);
}

.eyebrow span {
  display: inline-flex;
  min-height: 22px;
  align-items: center;
  padding: 1px 7px;
  color: var(--teal-dark);
  background: var(--teal-pale);
  border-radius: 3px;
}

h1,
h2 {
  font-family: var(--serif);
  font-weight: 500;
}

.hero h1 {
  margin: 25px 0 20px;
  font-size: clamp(2.8rem, 5vw, 5rem);
  letter-spacing: -0.055em;
  line-height: 1.02;
}

.hero-lede {
  max-width: 680px;
  margin: 0;
  color: var(--ink-soft);
  font-size: 1.06rem;
  line-height: 1.82;
}

.hero-actions,
.download-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin-top: 27px;
}

.button {
  display: inline-flex;
  min-height: 44px;
  align-items: center;
  justify-content: center;
  padding: 9px 16px;
  border: 1px solid transparent;
  border-radius: 4px;
  font-size: 0.79rem;
  font-weight: 800;
  text-decoration: none;
}

.button-primary {
  color: white;
  background: var(--ink);
}

.button-primary:hover {
  color: white;
  background: var(--teal-dark);
}

.button-secondary {
  color: var(--ink);
  background: var(--surface);
  border-color: var(--border-strong);
}

.button-secondary:hover {
  color: var(--ink);
  background: var(--teal-pale);
}

.snapshot-card {
  padding: 28px;
  color: white;
  background: var(--ink);
  box-shadow: 0 20px 50px rgba(19, 41, 75, 0.14);
}

.snapshot-head {
  display: flex;
  justify-content: space-between;
  gap: 18px;
  padding-bottom: 14px;
  border-bottom: 1px solid #466077;
}

.snapshot-head span {
  color: #9fdad2;
  font-family: var(--mono);
  font-size: 0.68rem;
  letter-spacing: 0.07em;
  text-transform: uppercase;
}

.snapshot-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1px;
  margin-top: 20px;
  background: #466077;
}

.snapshot-grid div {
  padding: 14px;
  background: var(--ink);
}

.snapshot-grid span,
.snapshot-grid strong {
  display: block;
}

.snapshot-grid span {
  color: #b9cbd7;
  font-size: 0.67rem;
  font-weight: 700;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.snapshot-grid strong {
  margin-top: 4px;
  font-family: var(--serif);
  font-size: 1.45rem;
}

.snapshot-note {
  margin: 18px 0 0;
  color: #c3d2dd;
  font-size: 0.75rem;
}

.section-intro {
  max-width: 850px;
}

.section-intro h2,
.section-head h2 {
  margin: 16px 0 14px;
  font-size: clamp(2rem, 3.2vw, 3.3rem);
  letter-spacing: -0.035em;
  line-height: 1.12;
}

.section-intro p,
.section-head p {
  margin: 0;
  color: var(--ink-soft);
}

.section-head {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: 24px;
  align-items: end;
}

.status-chip {
  padding: 9px 12px;
  color: var(--teal-dark);
  background: var(--teal-pale);
  border: 1px solid #aad4cb;
  font-family: var(--mono);
  font-size: 0.67rem;
  font-weight: 800;
  white-space: nowrap;
}

.metric-grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 1px;
  margin: 30px 0;
  background: var(--border);
  border: 1px solid var(--border);
}

.metric-grid article {
  padding: 20px;
  background: var(--surface);
}

.metric-grid span {
  display: block;
  color: var(--muted);
  font-size: 0.68rem;
  font-weight: 800;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.metric-grid strong {
  display: block;
  margin-top: 6px;
  font-family: var(--serif);
  font-size: 1.55rem;
}

.callout {
  margin: 28px 0;
  padding: 20px 22px;
  background: var(--surface-alt);
  border-left: 4px solid var(--teal);
}

.callout.warning {
  background: var(--red-pale);
  border-color: var(--red);
}

.callout strong {
  display: block;
  margin-bottom: 6px;
}

.callout p {
  margin: 0;
  color: var(--ink-soft);
}

.two-column {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 26px;
  align-items: start;
}

.two-column h3,
.method-block h3,
.risk-block h3 {
  margin: 0 0 9px;
  font-family: var(--serif);
  font-size: 1.35rem;
}

.two-column p,
.method-block p,
.risk-block p {
  color: var(--ink-soft);
}

.table-wrap {
  overflow-x: auto;
  margin: 28px 0;
  background: var(--surface);
  border: 1px solid var(--border);
}

table {
  width: 100%;
  min-width: 700px;
  border-collapse: collapse;
  font-size: 0.82rem;
}

caption {
  padding: 13px 16px;
  color: var(--muted);
  background: var(--surface-alt);
  border-bottom: 1px solid var(--border);
  font-size: 0.7rem;
  font-weight: 800;
  letter-spacing: 0.06em;
  text-align: left;
  text-transform: uppercase;
}

th,
td {
  padding: 12px 14px;
  border-bottom: 1px solid var(--border);
  text-align: right;
}

th:first-child,
td:first-child {
  text-align: left;
}

thead th {
  color: var(--muted);
  background: #f5f7f5;
  font-size: 0.67rem;
  text-transform: uppercase;
}

tbody tr:last-child th,
tbody tr:last-child td {
  border-bottom: 0;
}

.figure-panel {
  margin: 32px 0;
  padding: 16px;
  background: var(--surface);
  border: 1px solid var(--border);
}

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

.figure-panel figcaption {
  padding: 12px 2px 0;
  color: var(--muted);
  font-size: 0.75rem;
}

.formula {
  margin: 22px 0;
  padding: 20px;
  color: white;
  background: var(--ink);
  font-family: var(--serif);
  font-size: 1.08rem;
  line-height: 1.65;
}

.method-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 14px;
  margin-top: 26px;
}

.method-block {
  padding: 20px;
  background: var(--surface);
  border-top: 2px solid var(--teal);
}

.method-block p {
  margin: 0;
  font-size: 0.84rem;
}

.decision-list {
  margin: 24px 0;
  padding: 0;
  list-style: none;
  counter-reset: decision;
}

.decision-list li {
  position: relative;
  padding: 13px 0 13px 42px;
  border-bottom: 1px solid var(--border);
  counter-increment: decision;
}

.decision-list li::before {
  position: absolute;
  left: 0;
  color: var(--teal);
  content: counter(decision, decimal-leading-zero);
  font-family: var(--mono);
  font-size: 0.72rem;
  font-weight: 800;
}

.risk-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 18px;
}

.risk-grid article {
  padding: 22px;
  background: var(--surface);
  border: 1px solid var(--border);
}

.download-strip {
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 24px;
  align-items: center;
  padding: 26px;
  color: white;
  background: var(--ink);
}

.download-strip h3 {
  margin: 0 0 5px;
  color: white;
  font-family: var(--serif);
  font-size: 1.4rem;
}

.download-strip p {
  margin: 0;
  color: #c7d4de;
  font-size: 0.84rem;
}

.site-footer {
  width: min(100%, var(--width));
  margin: 0 auto;
  padding: 32px 54px 56px;
  color: var(--muted);
  font-size: 0.74rem;
}

.site-footer strong {
  color: var(--ink);
  font-family: var(--serif);
  font-size: 1rem;
}

.footer-links {
  display: flex;
  flex-wrap: wrap;
  gap: 16px;
  margin-top: 10px;
}

.reveal {
  opacity: 0;
  transform: translateY(10px);
  transition: opacity 320ms ease, transform 320ms ease;
}

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

@media (max-width: 1000px) {
  .site-shell { display: block; }
  .menu-button { display: grid; place-items: center; }
  .sidebar {
    position: fixed;
    z-index: 80;
    top: var(--topbar);
    bottom: 0;
    left: 0;
    width: min(88vw, 330px);
    height: auto;
    transform: translateX(-105%);
    transition: transform 220ms ease;
  }
  .nav-open .sidebar {
    transform: translateX(0);
    box-shadow: 20px 0 50px rgba(19, 41, 75, 0.16);
  }
  body.nav-open { overflow: hidden; }
  .chapter { padding-right: 36px; padding-left: 36px; }
}

@media (max-width: 760px) {
  :root { --topbar: 60px; }
  .topbar { padding: 0 16px; }
  .topbar-meta span { display: none; }
  .chapter { padding: 58px 20px; }
  .hero { grid-template-columns: 1fr; min-height: auto; padding-top: 38px; }
  .hero h1 { font-size: clamp(2.55rem, 13vw, 4.1rem); }
  .metric-grid,
  .method-grid,
  .risk-grid,
  .two-column { grid-template-columns: 1fr; }
  .section-head { grid-template-columns: 1fr; }
  .status-chip { justify-self: start; white-space: normal; }
  .download-strip { grid-template-columns: 1fr; }
  .site-footer { padding: 28px 20px 46px; }
}

@media (max-width: 430px) {
  .snapshot-grid { grid-template-columns: 1fr; }
  .hero-actions .button,
  .download-actions .button { width: 100%; }
}

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

@media print {
  .topbar, .sidebar, .reading-progress, .mobile-scrim, .hero-actions { display: none !important; }
  .site-shell { display: block; padding-top: 0; }
  .chapter { width: 100%; padding: 26px 0; break-inside: avoid; }
  body { background: white; font-size: 10pt; }
  .figure-panel img { max-height: 420px; object-fit: contain; }
}