:root {
  --bg: #f5f1e8;
  --ink: #13201d;
  --muted: #62706b;
  --surface: #fffdf7;
  --surface-strong: #ffffff;
  --line: #d9d0bf;
  --teal: #156f73;
  --teal-dark: #0d4c52;
  --coral: #c65b47;
  --gold: #d9a441;
  --sage: #71896f;
  --blue: #3c6382;
  --shadow: 0 20px 60px rgba(25, 37, 34, 0.14);
  --radius: 8px;
  --header-height: 72px;
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  min-height: 100vh;
  background:
    linear-gradient(120deg, rgba(21, 111, 115, 0.08), transparent 36%),
    linear-gradient(240deg, rgba(217, 164, 65, 0.12), transparent 38%),
    var(--bg);
  color: var(--ink);
  font-size: 16px;
  line-height: 1.5;
}

button,
input {
  font: inherit;
}

button {
  cursor: pointer;
}

img {
  display: block;
  max-width: 100%;
}

.sr-only,
.skip-link:not(:focus) {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

.skip-link:focus {
  position: fixed;
  z-index: 50;
  top: 12px;
  left: 12px;
  padding: 10px 14px;
  border-radius: var(--radius);
  background: var(--ink);
  color: #fff;
}

.app-header {
  position: sticky;
  top: 0;
  z-index: 30;
  background: rgba(245, 241, 232, 0.9);
  border-bottom: 1px solid rgba(217, 208, 191, 0.8);
  backdrop-filter: blur(18px);
}

.app-header[data-elevated="true"] {
  box-shadow: 0 12px 34px rgba(19, 32, 29, 0.08);
}

.header-inner {
  width: min(1180px, calc(100% - 32px));
  min-height: var(--header-height);
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 18px;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 12px;
  color: inherit;
  text-decoration: none;
  font-weight: 850;
  letter-spacing: 0;
}

.brand-mark {
  width: 42px;
  height: 42px;
  border-radius: 50%;
  background:
    radial-gradient(circle at 50% 50%, var(--surface) 0 20%, transparent 22%),
    conic-gradient(from 30deg, var(--teal), var(--gold), var(--coral), var(--blue), var(--teal));
  border: 1px solid rgba(19, 32, 29, 0.14);
}

.header-actions {
  display: flex;
  gap: 8px;
}

.icon-button {
  width: 44px;
  height: 44px;
  display: inline-grid;
  place-items: center;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--surface);
  color: var(--ink);
  font-weight: 800;
}

.icon-button:hover,
.icon-button:focus-visible,
.control-button:hover,
.control-button:focus-visible,
.primary-action:hover,
.primary-action:focus-visible,
.ghost-action:hover,
.ghost-action:focus-visible {
  outline: 3px solid rgba(21, 111, 115, 0.22);
  outline-offset: 2px;
}

.progress-track {
  height: 4px;
  background: rgba(19, 32, 29, 0.08);
}

.progress-track span {
  display: block;
  width: 0%;
  height: 100%;
  background: linear-gradient(90deg, var(--teal), var(--gold), var(--coral));
  transition: width 250ms ease;
}

.terms-panel {
  position: fixed;
  z-index: 45;
  top: calc(var(--header-height) + 14px);
  right: 16px;
  width: min(420px, calc(100% - 32px));
  max-height: calc(100svh - var(--header-height) - 38px);
  overflow: auto;
  padding: 18px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--surface-strong);
  box-shadow: var(--shadow);
}

.terms-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 10px;
}

.terms-header h2 {
  margin: 0;
  font-size: 1.15rem;
}

.terms-list {
  display: grid;
  gap: 10px;
}

.term-item {
  padding: 12px;
  border-left: 4px solid var(--teal);
  background: #f7fbf7;
}

.term-item strong {
  display: block;
  margin-bottom: 2px;
}

.term-item p {
  margin: 0;
  color: var(--muted);
  font-size: 0.92rem;
}

.story {
  min-height: calc(100svh - var(--header-height));
}

.screen {
  display: none;
  min-height: calc(100svh - var(--header-height) - 80px);
  width: min(1180px, calc(100% - 32px));
  margin: 0 auto;
  padding: clamp(28px, 5vh, 64px) 0 104px;
}

.screen.is-active {
  display: block;
  animation: screenIn 420ms ease both;
}

@keyframes screenIn {
  from {
    opacity: 0;
    transform: translateY(10px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.hero-screen,
.screen-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(360px, 0.95fr);
  gap: clamp(28px, 6vw, 72px);
  align-items: center;
}

.hero-copy,
.copy-column {
  max-width: 640px;
}

.eyebrow {
  margin: 0 0 10px;
  color: var(--teal-dark);
  font-size: 0.78rem;
  font-weight: 900;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

h1,
h2,
h3,
p {
  overflow-wrap: anywhere;
}

h1,
h2,
h3 {
  margin: 0;
  line-height: 1.04;
  letter-spacing: 0;
}

h1 {
  max-width: 780px;
  font-size: clamp(2.9rem, 7vw, 6.2rem);
}

h2 {
  font-size: clamp(2.2rem, 5.2vw, 4.5rem);
}

h3 {
  font-size: 1.15rem;
}

p {
  color: var(--muted);
}

.lead {
  max-width: 620px;
  margin: 20px 0 0;
  font-size: clamp(1.05rem, 2vw, 1.28rem);
}

.definition-strip,
.definition-card,
.takeaway-card,
.mode-panel,
.metric-block,
.choice-card,
.data-house,
.round-display,
.after-training,
.final-takeaway {
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: rgba(255, 253, 247, 0.92);
}

.definition-strip {
  display: grid;
  gap: 4px;
  margin: 28px 0;
  padding: 16px;
}

.definition-strip strong {
  color: var(--teal-dark);
}

.definition-strip span,
.definition-card p,
.takeaway-card p {
  color: var(--muted);
}

.primary-action,
.ghost-action,
.control-button {
  min-height: 46px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  border-radius: var(--radius);
  font-weight: 850;
  letter-spacing: 0;
}

.primary-action {
  padding: 13px 19px;
  border: 1px solid var(--teal-dark);
  background: var(--teal);
  color: #fff;
}

.ghost-action {
  padding: 13px 19px;
  border: 1px solid var(--line);
  background: var(--surface);
  color: var(--ink);
}

.house-card {
  overflow: hidden;
  box-shadow: var(--shadow);
}

.feature-house {
  align-self: start;
  margin-top: clamp(24px, 18vh, 138px);
}

.feature-house img {
  width: 100%;
  aspect-ratio: 1.9;
  object-fit: cover;
}

.house-card-body {
  padding: 18px;
  background: var(--surface-strong);
}

.tag {
  display: inline-flex;
  margin-bottom: 12px;
  color: var(--teal-dark);
  font-weight: 900;
  text-transform: uppercase;
  letter-spacing: 0.09em;
  font-size: 0.78rem;
}

dl {
  margin: 0;
  display: grid;
  gap: 10px;
}

dl div {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 14px;
}

dt {
  color: var(--muted);
}

dd {
  margin: 0;
  font-weight: 850;
}

.hidden-price {
  color: var(--coral);
}

.definition-card {
  padding: 16px;
}

.definition-card h3 {
  margin-bottom: 8px;
}

.definition-card p {
  margin: 0;
}

.equation {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 10px;
  margin: 24px 0 10px;
  font-size: clamp(1.6rem, 4vw, 2.7rem);
  font-weight: 900;
}

.equation button {
  min-width: 54px;
  min-height: 54px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--surface-strong);
  color: var(--teal-dark);
  font-size: inherit;
  font-weight: inherit;
}

.equation button.is-selected {
  border-color: var(--teal);
  background: rgba(21, 111, 115, 0.1);
}

.symbol-help {
  min-height: 28px;
  margin: 0;
  color: var(--teal-dark);
  font-weight: 700;
}

.interactive-panel,
.training-panel {
  padding: clamp(18px, 3vw, 28px);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: rgba(255, 253, 247, 0.78);
  box-shadow: var(--shadow);
}

.neuron-flow {
  display: grid;
  grid-template-columns: 1fr;
  justify-items: center;
  gap: 10px;
}

.flow-node {
  width: min(100%, 280px);
  padding: 14px;
  text-align: center;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--surface-strong);
}

.flow-node span,
.metric-block span,
.round-display span {
  display: block;
  color: var(--muted);
  font-size: 0.86rem;
  font-weight: 800;
  text-transform: uppercase;
  letter-spacing: 0.08em;
}

.flow-node strong,
.metric-block strong,
.round-display strong {
  display: block;
  margin-top: 4px;
  font-size: 1.35rem;
}

.flow-link {
  width: 2px;
  height: 26px;
  background: linear-gradient(var(--teal), var(--gold));
}

.neuron {
  width: 156px;
  height: 156px;
  display: grid;
  place-items: center;
  position: relative;
  border-radius: 50%;
  color: var(--teal-dark);
  background:
    radial-gradient(circle at 50% 50%, var(--surface) 0 48%, transparent 49%),
    conic-gradient(from 0deg, var(--teal), var(--gold), var(--coral), var(--blue), var(--teal));
  box-shadow: inset 0 0 0 1px rgba(19, 32, 29, 0.12), 0 12px 34px rgba(21, 111, 115, 0.18);
}

.neuron span {
  position: absolute;
  width: 92px;
  height: 92px;
  border: 1px solid rgba(21, 111, 115, 0.25);
  border-radius: 50%;
}

.neuron strong {
  position: relative;
}

.slider-grid {
  display: grid;
  gap: 18px;
  margin-top: 24px;
}

.slider-grid label {
  display: grid;
  gap: 8px;
  font-weight: 800;
}

.slider-grid label span {
  display: flex;
  justify-content: space-between;
  gap: 18px;
}

input[type="range"] {
  width: 100%;
  accent-color: var(--teal);
}

.takeaway {
  margin: 18px 0 0;
  color: var(--teal-dark);
  font-weight: 850;
}

.center-stack,
.question-screen,
.final-screen {
  min-height: 64svh;
  display: grid;
  align-content: center;
  justify-items: center;
  text-align: center;
  gap: 22px;
}

.narrow {
  max-width: 760px;
  margin: 0;
  font-size: 1.1rem;
}

.comparison-layout {
  width: min(920px, 100%);
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 14px;
}

.metric-block {
  padding: clamp(18px, 3vw, 28px);
}

.metric-block.actual {
  border-top: 6px solid var(--sage);
}

.metric-block.predicted {
  border-top: 6px solid var(--blue);
}

.metric-block.error {
  border-top: 6px solid var(--coral);
}

.error-scale {
  width: min(760px, 100%);
  display: grid;
  grid-template-columns: auto minmax(120px, 1fr) auto;
  align-items: center;
  gap: 12px;
  color: var(--muted);
  font-weight: 800;
}

.error-scale div {
  height: 12px;
  border-radius: 999px;
  background: linear-gradient(90deg, var(--coral), var(--gold), var(--sage));
  overflow: hidden;
}

.error-scale i {
  display: block;
  width: 36%;
  height: 100%;
  background: rgba(255, 255, 255, 0.58);
}

.definition-row {
  width: min(900px, 100%);
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 14px;
}

.choice-grid {
  width: min(940px, 100%);
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 14px;
}

.choice-card {
  min-height: 180px;
  display: grid;
  place-items: center;
  gap: 12px;
  padding: 18px;
}

.choice-card span {
  width: 52px;
  height: 52px;
  display: grid;
  place-items: center;
  border-radius: 50%;
  color: #fff;
  font-weight: 900;
  font-size: 1.3rem;
}

.choice-card.rejected span {
  background: var(--coral);
}

.choice-card.accepted {
  border-color: rgba(21, 111, 115, 0.45);
  background: rgba(21, 111, 115, 0.08);
}

.choice-card.accepted span {
  background: var(--teal);
}

.loop-grid {
  grid-template-columns: minmax(300px, 0.82fr) minmax(420px, 1fr);
}

.definition-stack {
  display: grid;
  gap: 12px;
  margin-top: 22px;
}

.definition-stack.compact .definition-card {
  padding: 14px;
}

.learning-loop {
  position: relative;
  width: min(560px, 100%);
  aspect-ratio: 1;
  margin-inline: auto;
}

.loop-ring {
  position: absolute;
  inset: 14%;
  border: 16px solid rgba(21, 111, 115, 0.13);
  border-top-color: var(--teal);
  border-right-color: var(--gold);
  border-radius: 50%;
  animation: rotateLoop 8s linear infinite;
}

@keyframes rotateLoop {
  to {
    transform: rotate(360deg);
  }
}

.loop-step {
  --angle: calc(var(--i) * 60deg - 90deg);
  position: absolute;
  left: 50%;
  top: 50%;
  width: 142px;
  min-height: 74px;
  display: grid;
  place-items: center;
  padding: 10px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--surface-strong);
  box-shadow: 0 10px 28px rgba(19, 32, 29, 0.08);
  transform: rotate(var(--angle)) translate(198px) rotate(calc(-1 * var(--angle))) translate(-50%, -50%);
}

.loop-step strong {
  font-size: 0.86rem;
}

.takeaway-card {
  margin-top: 22px;
  padding: 18px;
  border-left: 6px solid var(--gold);
}

.takeaway-card p {
  margin: 0;
  color: var(--ink);
  font-size: 1.06rem;
  font-weight: 850;
}

.round-display {
  display: grid;
  gap: 6px;
  padding: 18px;
  margin-bottom: 16px;
  text-align: center;
}

.round-display em {
  color: var(--coral);
  font-style: normal;
  font-weight: 900;
}

.error-chart {
  width: 100%;
  height: auto;
  overflow: visible;
}

.error-chart line {
  stroke: rgba(19, 32, 29, 0.3);
  stroke-width: 2;
}

.error-chart text {
  fill: var(--muted);
  font-size: 14px;
  font-weight: 800;
}

#errorLine {
  fill: none;
  stroke: var(--teal);
  stroke-width: 5;
  stroke-linecap: round;
  stroke-linejoin: round;
}

#errorDots circle {
  fill: var(--surface-strong);
  stroke: var(--teal);
  stroke-width: 4;
}

.house-data-grid {
  width: min(1020px, 100%);
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 14px;
}

.data-house {
  overflow: hidden;
  text-align: left;
}

.data-house img {
  width: 100%;
  aspect-ratio: 1.05;
  object-fit: cover;
}

.data-house strong,
.data-house span {
  display: block;
  padding-inline: 14px;
}

.data-house strong {
  padding-top: 12px;
  font-size: 1.05rem;
}

.data-house span {
  padding-bottom: 14px;
  color: var(--muted);
  font-weight: 800;
}

.data-house.active {
  outline: 4px solid rgba(21, 111, 115, 0.2);
}

.wide-definition {
  width: min(760px, 100%);
  text-align: left;
}

.process-line {
  width: min(900px, 100%);
  padding: 16px;
  border-radius: var(--radius);
  background: var(--ink);
  color: #fff;
  font-weight: 900;
}

.network-diagram {
  min-height: 520px;
  display: grid;
  grid-template-columns: 0.65fr 0.35fr 0.44fr 0.5fr 0.72fr;
  align-items: center;
  gap: 12px;
  padding: 18px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: rgba(255, 253, 247, 0.78);
  box-shadow: var(--shadow);
}

.input-stack {
  display: grid;
  gap: 12px;
}

.input-stack span,
.network-output {
  display: grid;
  place-items: center;
  min-height: 54px;
  padding: 10px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--surface-strong);
  font-weight: 850;
}

.connector-field {
  height: 80%;
  background:
    linear-gradient(18deg, transparent 47%, rgba(21, 111, 115, 0.32) 48% 52%, transparent 53%),
    linear-gradient(-18deg, transparent 47%, rgba(60, 99, 130, 0.28) 48% 52%, transparent 53%),
    linear-gradient(0deg, transparent 47%, rgba(217, 164, 65, 0.28) 48% 52%, transparent 53%);
}

.layer {
  display: grid;
  justify-items: center;
  gap: 20px;
}

.layer i {
  width: 70px;
  height: 70px;
  border-radius: 50%;
  background:
    radial-gradient(circle at 50% 50%, var(--surface) 0 48%, transparent 49%),
    conic-gradient(var(--teal), var(--gold), var(--coral), var(--teal));
  border: 1px solid rgba(19, 32, 29, 0.14);
}

.hidden-layer i {
  width: 62px;
  height: 62px;
}

.network-output {
  min-height: 96px;
  color: #fff;
  background: var(--teal-dark);
  border-color: var(--teal-dark);
}

.split-panels {
  width: min(920px, 100%);
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 18px;
  text-align: left;
}

.mode-panel {
  padding: clamp(18px, 3vw, 28px);
  border-top: 6px solid var(--gold);
}

.mode-panel.inference {
  border-top-color: var(--teal);
}

.mode-panel ol {
  margin: 18px 0;
  padding-left: 22px;
  color: var(--muted);
  font-weight: 800;
}

.mode-panel li + li {
  margin-top: 8px;
}

.mode-panel p {
  margin: 14px 0 0;
}

.answer-actions {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 12px;
}

.overfit-result {
  width: min(920px, 100%);
  display: grid;
  gap: 16px;
}

.generalization-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 14px;
}

.generalization-grid article {
  padding: 18px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--surface-strong);
}

.generalization-grid p {
  margin: 10px 0 16px;
}

.checks {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  color: var(--teal-dark);
  font-weight: 900;
}

.checks.mixed {
  color: var(--coral);
}

.final-screen {
  gap: 24px;
}

.final-flow {
  width: min(1050px, 100%);
  display: grid;
  grid-template-columns: repeat(7, minmax(0, 1fr));
  gap: 8px;
}

.final-flow span {
  min-height: 84px;
  display: grid;
  place-items: center;
  padding: 10px;
  border-radius: var(--radius);
  color: #fff;
  background: var(--teal-dark);
  font-weight: 900;
}

.final-flow span:nth-child(2n) {
  background: var(--blue);
}

.final-flow span:nth-child(3n) {
  background: var(--coral);
}

.final-flow span:nth-child(5) {
  background: var(--gold);
  color: var(--ink);
}

.final-takeaway,
.after-training {
  width: min(860px, 100%);
  padding: 18px;
}

.final-takeaway strong {
  font-size: clamp(1.3rem, 3vw, 2.3rem);
}

.after-training {
  display: grid;
  gap: 6px;
}

.after-training span {
  color: var(--muted);
  font-weight: 850;
  text-transform: uppercase;
  letter-spacing: 0.08em;
}

.closing-line {
  max-width: 880px;
  margin: 0;
  color: var(--teal-dark);
  font-size: clamp(1.1rem, 2.2vw, 1.35rem);
  font-weight: 850;
}

.story-controls {
  position: fixed;
  z-index: 35;
  right: 24px;
  bottom: 18px;
  display: flex;
  gap: 8px;
  padding: 8px;
  border: 1px solid rgba(217, 208, 191, 0.92);
  border-radius: var(--radius);
  background: rgba(255, 253, 247, 0.92);
  box-shadow: 0 14px 40px rgba(19, 32, 29, 0.14);
  backdrop-filter: blur(18px);
}

.control-button {
  padding: 10px 14px;
  border: 1px solid transparent;
  background: transparent;
  color: var(--ink);
  white-space: nowrap;
}

.control-button[aria-pressed="true"],
.control-button:not(:disabled):hover {
  background: rgba(21, 111, 115, 0.09);
  border-color: rgba(21, 111, 115, 0.18);
}

.control-button:disabled {
  cursor: not-allowed;
  opacity: 0.45;
}

@media (max-width: 900px) {
  .hero-screen,
  .screen-grid,
  .loop-grid {
    grid-template-columns: 1fr;
  }

  .hero-copy,
  .copy-column {
    max-width: none;
  }

  .feature-house img {
    aspect-ratio: 1.38;
  }

  .feature-house {
    margin-top: 0;
  }

  .comparison-layout,
  .choice-grid,
  .house-data-grid,
  .split-panels,
  .generalization-grid {
    grid-template-columns: 1fr 1fr;
  }

  .network-diagram {
    grid-template-columns: 1fr;
    min-height: auto;
  }

  .connector-field {
    height: 50px;
  }

  .layer {
    grid-template-columns: repeat(4, 1fr);
  }

  .layer i {
    width: 56px;
    height: 56px;
  }

  .final-flow {
    grid-template-columns: repeat(4, minmax(0, 1fr));
  }
}

@media (max-width: 620px) {
  :root {
    --header-height: 64px;
  }

  .header-inner,
  .screen {
    width: min(100% - 24px, 1180px);
  }

  .brand span:last-child {
    font-size: 0.95rem;
  }

  .brand-mark {
    width: 36px;
    height: 36px;
  }

  .icon-button {
    width: 40px;
    height: 40px;
  }

  h1 {
    font-size: clamp(2.35rem, 14vw, 3.6rem);
  }

  h2 {
    font-size: clamp(2rem, 10vw, 3rem);
  }

  .screen {
    padding-bottom: 118px;
  }

  .comparison-layout,
  .choice-grid,
  .house-data-grid,
  .definition-row,
  .split-panels,
  .generalization-grid,
  .final-flow {
    grid-template-columns: 1fr;
  }

  .error-scale {
    grid-template-columns: 1fr;
  }

  .learning-loop {
    aspect-ratio: auto;
    display: grid;
    gap: 10px;
  }

  .loop-ring {
    display: none;
  }

  .loop-step {
    position: static;
    width: 100%;
    min-height: 58px;
    transform: none;
  }

  .story-controls {
    width: calc(100% - 20px);
    left: 50%;
    right: auto;
    justify-content: space-between;
    transform: translateX(-50%);
  }

  .control-button {
    flex: 1;
    padding-inline: 8px;
  }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    scroll-behavior: auto !important;
    transition-duration: 0.01ms !important;
  }
}