:root {
  --paper: #f3ede1;
  --paper-2: #ebe3d2;
  --paper-3: #e2d8c2;
  --card: #fbf7ec;
  --ink: #1a1814;
  --ink-2: #3a352c;
  --muted: #6f6754;
  --line: #cfc4ac;
  --line-2: #b8ab8e;
  --accent: #6b4f1d;
  --accent-soft: #c9a566;
  --accent-wash: #efe3c7;
  --fit: #2a5d57;
  --fit-wash: #dde9e6;
  --student: #8a3a1f;
  --student-wash: #ecd6c8;
  --serif: "Source Serif 4", "Iowan Old Style", "Charter", Georgia, serif;
  --sans: "Manrope", ui-sans-serif, system-ui, -apple-system, "Segoe UI", sans-serif;
  --mono: "JetBrains Mono", ui-monospace, "SF Mono", Menlo, monospace;
  --r-sm: 4px;
  --r-md: 8px;
  --r-lg: 14px;
  color-scheme: light;
}

* { box-sizing: border-box; }
html, body { margin: 0; padding: 0; overflow-x: hidden; }
body {
  background: var(--paper);
  color: var(--ink);
  font-family: var(--sans);
  font-size: 15px;
  line-height: 1.5;
  -webkit-font-smoothing: antialiased;
}
body::before {
  content: "";
  position: fixed;
  inset: 0;
  pointer-events: none;
  opacity: 0.35;
  mix-blend-mode: multiply;
  background-image: url("data:image/svg+xml;utf8,<svg xmlns='http://www.w3.org/2000/svg' width='240' height='240'><filter id='n'><feTurbulence type='fractalNoise' baseFrequency='0.9' numOctaves='2' stitchTiles='stitch'/><feColorMatrix values='0 0 0 0 0.1  0 0 0 0 0.09  0 0 0 0 0.07  0 0 0 0.06 0'/></filter><rect width='100%' height='100%' filter='url(%23n)'/></svg>");
  z-index: 0;
}

button, input { font: inherit; color: inherit; }
button { cursor: pointer; }
button:disabled { cursor: not-allowed; opacity: 0.45; }
a { color: var(--accent); text-decoration: none; border-bottom: 1px solid currentColor; }
h1, h2, h3 { margin: 0; font-weight: 500; line-height: 1.1; letter-spacing: -0.01em; }
h1, h2 { font-family: var(--serif); font-weight: 400; }
h1 { max-width: 14ch; font-size: clamp(42px, 6vw, 72px); letter-spacing: -0.02em; }
h1 em { color: var(--accent); font-style: italic; }
h2 { font-size: clamp(30px, 3vw, 42px); }
p { margin: 0; }

.app {
  position: relative;
  z-index: 1;
  max-width: 1340px;
  margin: 0 auto;
  padding: 28px clamp(20px, 3vw, 40px) 80px;
}
.topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
  padding-bottom: 18px;
  border-bottom: 1px solid var(--line);
  margin-bottom: 42px;
}
.brand {
  display: flex;
  align-items: center;
  gap: 14px;
  color: inherit;
  border-bottom: 0;
}
.brand-mark {
  display: inline-grid;
  place-items: center;
  width: 36px;
  height: 36px;
  border: 1.5px solid var(--ink);
  border-radius: 50%;
  background: var(--card);
  font-family: var(--serif);
  font-size: 18px;
  font-style: italic;
}
.brand-name {
  display: block;
  font-family: var(--serif);
  font-size: 19px;
  line-height: 1.1;
}
.brand-meta {
  display: block;
  color: var(--muted);
  font-family: var(--mono);
  font-size: 12px;
}
.topbar-right {
  display: flex;
  flex-wrap: wrap;
  gap: 18px;
  color: var(--muted);
  font-family: var(--mono);
  font-size: 12px;
}
.topbar-right a { color: var(--muted); border-bottom-color: transparent; }
.topbar-right a:hover { color: var(--ink); border-bottom-color: var(--ink); }

.kicker {
  color: var(--muted);
  font-family: var(--mono);
  font-size: 11px;
  font-weight: 500;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}
.kicker--accent { color: var(--accent); }
.surface {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--r-lg);
  min-width: 0;
}

.hero {
  display: grid;
  grid-template-columns: minmax(0, 1.35fr) minmax(320px, 0.65fr);
  gap: 48px;
  align-items: end;
  padding-bottom: 40px;
  border-bottom: 1px solid var(--line);
  margin-bottom: 54px;
}
.hero-sub {
  max-width: 44ch;
  margin-top: 22px;
  color: var(--muted);
  font-family: var(--serif);
  font-size: clamp(18px, 2vw, 22px);
  font-style: italic;
  line-height: 1.45;
  overflow-wrap: anywhere;
}
.brief { padding: 22px; }
.brief p {
  margin-top: 10px;
  color: var(--ink-2);
  font-size: 14px;
}
.brief-flow {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 6px;
  margin-top: 18px;
}
.brief-flow span {
  min-height: 46px;
  display: grid;
  place-items: center;
  padding: 8px;
  background: var(--paper-2);
  border: 1px solid var(--line);
  border-radius: var(--r-md);
  color: var(--ink-2);
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.04em;
  text-align: center;
  text-transform: uppercase;
}

.module { margin-bottom: 64px; }
.module-head {
  display: grid;
  grid-template-columns: 64px minmax(0, 1fr) auto;
  gap: 20px;
  align-items: start;
  padding-bottom: 18px;
  border-bottom: 1px solid var(--line);
  margin-bottom: 28px;
}
.module-num {
  color: var(--accent);
  font-family: var(--serif);
  font-size: 38px;
  font-style: italic;
  line-height: 1;
  margin-top: 4px;
}
.module-title h2 { margin: 6px 0; }
.module-title { min-width: 0; }
.module-summary {
  max-width: 70ch;
  color: var(--muted);
  font-family: var(--serif);
  font-size: 17px;
  font-style: italic;
  overflow-wrap: anywhere;
}
.module-pattern {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  color: var(--muted);
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}
.module-pattern span {
  padding: 4px 8px;
  background: var(--paper-2);
  border-radius: var(--r-sm);
}
.module-pattern .on {
  color: var(--accent);
  background: var(--accent-wash);
}

.lab {
  display: grid;
  grid-template-columns: minmax(0, 1.55fr) minmax(300px, 1fr);
  gap: 24px;
  align-items: start;
}
.lab-main {
  display: grid;
  gap: 14px;
  min-width: 0;
}
.plot-wrap { overflow: hidden; }
.plot-wrap svg {
  display: block;
  width: 100%;
  height: auto;
  touch-action: none;
}
.plot-bg { fill: var(--card); }
.grid line {
  stroke: var(--line);
  stroke-width: 1;
  opacity: 0.7;
}
.axis {
  stroke: var(--ink);
  stroke-width: 1.6;
}
.ticks text,
.axis-label {
  fill: var(--muted);
  font-family: var(--mono);
  font-size: 12px;
  text-anchor: middle;
}
.axis-label {
  font-size: 11px;
  letter-spacing: 0.05em;
  text-transform: uppercase;
}
.residual {
  stroke: var(--student);
  stroke-width: 2;
  opacity: 0.32;
}
.student-line {
  stroke: var(--student);
  stroke-width: 4;
  stroke-linecap: round;
}
.fit-line {
  stroke: var(--fit);
  stroke-width: 4;
  stroke-linecap: round;
  stroke-dasharray: 10 8;
}
.point circle {
  fill: var(--ink);
  stroke: var(--card);
  stroke-width: 3;
}
.point text {
  fill: var(--muted);
  font-family: var(--mono);
  font-size: 11px;
}
.handle { cursor: grab; }
.handle:active { cursor: grabbing; }
.handle circle:first-child {
  fill: var(--student-wash);
  stroke: var(--student);
  stroke-width: 2;
}
.handle circle:last-child { fill: var(--student); }
.plot-footer {
  display: flex;
  justify-content: space-between;
  gap: 16px;
  padding: 12px 16px 14px;
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.04em;
  text-transform: uppercase;
}

.panel {
  display: grid;
  grid-template-columns: 1fr;
  gap: 14px;
}
.panel-section {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--r-lg);
  padding: 18px;
}
.button-row {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 12px;
}
.btn {
  min-height: 38px;
  padding: 8px 12px;
  background: var(--paper-2);
  border: 1px solid var(--line-2);
  border-radius: var(--r-md);
  color: var(--ink-2);
  font-weight: 600;
}
.btn:hover:not(:disabled) {
  border-color: var(--ink);
  color: var(--ink);
}
.btn-primary {
  background: var(--accent);
  border-color: var(--accent);
  color: var(--card);
}
.btn-primary:hover:not(:disabled) {
  background: var(--ink);
  color: var(--card);
}
.small-note {
  margin-top: 12px;
  color: var(--muted);
  font-size: 13px;
}
.metric {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: 12px;
  align-items: baseline;
  margin-top: 10px;
  padding: 10px 12px;
  background: var(--paper-2);
  border: 1px solid var(--line);
  border-radius: var(--r-md);
}
.metric span {
  color: var(--muted);
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}
.metric strong {
  font-family: var(--mono);
  font-size: 15px;
}
.metric--student { background: var(--student-wash); }
.metric--fit { background: var(--fit-wash); }
.check {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-top: 12px;
  min-height: 38px;
  padding: 8px 10px;
  background: var(--paper-2);
  border: 1px solid var(--line);
  border-radius: var(--r-md);
  color: var(--ink-2);
  font-size: 14px;
}
.check input {
  width: 18px;
  height: 18px;
  accent-color: var(--accent);
}
.equations {
  display: grid;
  gap: 10px;
}
.equations code {
  display: block;
  padding: 10px 12px;
  background: var(--paper-2);
  border: 1px solid var(--line);
  border-radius: var(--r-md);
  font-family: var(--mono);
  font-size: 12px;
  line-height: 1.4;
  white-space: normal;
}
.prompt ol {
  margin: 12px 0 0;
  padding-left: 20px;
  color: var(--ink-2);
}
.prompt li + li { margin-top: 8px; }

.segmented {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 6px;
  margin-top: 12px;
  padding: 4px;
  background: var(--paper-2);
  border: 1px solid var(--line);
  border-radius: var(--r-md);
}
.segmented button {
  min-height: 34px;
  background: transparent;
  border: 0;
  border-radius: var(--r-sm);
  color: var(--muted);
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.04em;
  text-transform: uppercase;
}
.segmented button.active {
  background: var(--card);
  color: var(--accent);
  box-shadow: inset 0 0 0 1px var(--line-2);
}

.cluster-link {
  stroke-width: 2;
  stroke-dasharray: 5 6;
  opacity: 0.35;
  transition: x2 520ms ease, y2 520ms ease, stroke 240ms ease, opacity 240ms ease;
}
.cluster-point circle {
  stroke: var(--card);
  stroke-width: 3;
  transition: fill 240ms ease;
}
.centroid {
  cursor: grab;
}
.centroid:active {
  cursor: grabbing;
}
.centroid circle {
  stroke: var(--ink);
  stroke-width: 2;
  transition: cx 620ms ease, cy 620ms ease, fill 240ms ease;
}
.centroid path {
  fill: none;
  stroke: var(--card);
  stroke-width: 3;
  stroke-linecap: round;
  transition: d 620ms ease;
}
.centroid text {
  fill: var(--ink);
  font-family: var(--mono);
  font-size: 12px;
  font-weight: 700;
  text-anchor: middle;
  transition: x 620ms ease, y 620ms ease;
}

.cluster-fill-0 circle { fill: #2a5d57; }
.cluster-fill-1 circle { fill: #8a3a1f; }
.cluster-fill-2 circle { fill: #6b4f1d; }
.cluster-fill-3 circle { fill: #395a88; }
.cluster-stroke-0 { stroke: #2a5d57; }
.cluster-stroke-1 { stroke: #8a3a1f; }
.cluster-stroke-2 { stroke: #6b4f1d; }
.cluster-stroke-3 { stroke: #395a88; }

.cluster-list {
  display: grid;
  gap: 10px;
}
.cluster-row {
  display: grid;
  grid-template-columns: 14px minmax(0, 1fr) auto;
  gap: 8px 10px;
  align-items: center;
  padding: 10px 12px;
  background: var(--paper-2);
  border: 1px solid var(--line);
  border-radius: var(--r-md);
}
.cluster-swatch {
  width: 12px;
  height: 12px;
  border-radius: 50%;
  background: var(--ink);
}
.cluster-row span:nth-child(2) {
  color: var(--ink-2);
  font-size: 13px;
  font-weight: 600;
}
.cluster-row strong {
  color: var(--muted);
  font-family: var(--mono);
  font-size: 11px;
  font-weight: 600;
  text-transform: uppercase;
}
.cluster-row code {
  grid-column: 2 / -1;
  color: var(--muted);
  font-family: var(--mono);
  font-size: 11px;
}
.cluster-0 .cluster-swatch { background: #2a5d57; }
.cluster-1 .cluster-swatch { background: #8a3a1f; }
.cluster-2 .cluster-swatch { background: #6b4f1d; }
.cluster-3 .cluster-swatch { background: #395a88; }

.resource-grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 20px;
}
.resource-card {
  display: grid;
  gap: 12px;
  min-height: 250px;
  padding: 22px;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--r-lg);
  color: inherit;
  text-decoration: none;
  transition: border-color 160ms ease, transform 160ms ease, background 160ms ease;
}
.resource-card:hover {
  transform: translateY(-2px);
  border-color: var(--accent);
  background: var(--accent-wash);
}
.resource-card h3 {
  max-width: 28ch;
  color: var(--ink);
  font-family: var(--serif);
  font-size: clamp(22px, 2.2vw, 30px);
  font-weight: 400;
  line-height: 1.12;
  overflow-wrap: anywhere;
}
.resource-card p {
  color: var(--ink-2);
  font-size: 14px;
  line-height: 1.55;
}
.resource-meta {
  align-self: end;
  width: fit-content;
  padding: 5px 9px;
  background: var(--paper-2);
  border: 1px solid var(--line);
  border-radius: var(--r-sm);
  color: var(--muted);
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}
.resource-note {
  max-width: 78ch;
  margin-top: 16px;
  padding: 14px 16px;
  background: var(--paper-2);
  border: 1px solid var(--line);
  border-radius: var(--r-md);
  color: var(--muted);
  font-size: 14px;
}

@media (max-width: 1200px) {
  .hero, .lab {
    grid-template-columns: 1fr;
  }
  .resource-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }
}

@media (max-width: 720px) {
  .app { padding-inline: 18px; }
  .topbar {
    align-items: flex-start;
    flex-wrap: wrap;
  }
  .topbar-right {
    width: 100%;
    gap: 10px 16px;
  }
  .module-head { grid-template-columns: 48px 1fr; }
  .module-pattern { grid-column: 1 / -1; }
  .brief-flow { grid-template-columns: repeat(2, 1fr); }
  .panel { grid-template-columns: 1fr; }
  .plot-footer { flex-direction: column; }
  .ticks text { font-size: 11px; }
  .resource-grid { grid-template-columns: 1fr; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { transition-duration: 0.01ms !important; animation-duration: 0.01ms !important; }
}