:root {
  --paper: #faf9f6;
  --white: #fff;
  --ink: #222b30;
  --muted: #59656b;
  --line: #d5dce0;
  --blue: #245b91;
  --tint: #edf4fa;
  --warm: #f2eee4;
  --radius: 8px;
}
* {
  box-sizing: border-box;
}
html {
  scroll-behavior: smooth;
  scroll-padding-top: 24px;
}
body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font:
    16px/1.55 -apple-system,
    BlinkMacSystemFont,
    "Segoe UI",
    sans-serif;
}
::selection {
  background: #c8dfef;
  color: #142f47;
}
a {
  color: var(--blue);
  text-underline-offset: 5px;
}
button,
select {
  font: inherit;
}
button,
a,
select,
summary {
  -webkit-tap-highlight-color: transparent;
}
button {
  cursor: pointer;
}
a:focus-visible,
button:focus-visible,
select:focus-visible,
summary:focus-visible {
  outline: 3px solid var(--blue);
  outline-offset: 4px;
}
h1,
h2,
h3,
p {
  margin: 0;
}
h1 {
  font-size: clamp(32px, 4.2vw, 50px);
  font-weight: 600;
  letter-spacing: -0.035em;
  line-height: 1.15;
}
h2 {
  font-size: 24px;
  font-weight: 600;
  letter-spacing: -0.02em;
  line-height: 1.3;
}
h3 {
  font-size: 16px;
  font-weight: 600;
}
p {
  color: var(--muted);
}
.symbol-bank {
  position: absolute;
  width: 0;
  height: 0;
  overflow: hidden;
}
.skip {
  position: absolute;
  left: 20px;
  top: -80px;
  background: white;
  padding: 12px;
  z-index: 10;
}
.skip:focus {
  top: 12px;
}
.site-header {
  max-width: 1200px;
  margin: auto;
  padding: 24px 32px;
  display: flex;
  justify-content: space-between;
  align-items: center;
  border-bottom: 1px solid var(--line);
}
.wordmark {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 16px;
  font-weight: 600;
  color: var(--ink);
  text-decoration: none;
}
.site-header nav {
  display: flex;
  gap: 28px;
  font-size: 14px;
}
.site-header nav a {
  color: var(--muted);
  text-decoration: none;
}
.site-header a:hover,
footer a:hover {
  text-decoration: underline;
}
main {
  max-width: 1200px;
  padding: 0 32px;
  margin: auto;
}
.intro {
  padding: 64px 0 48px;
  max-width: 720px;
}
.intro p {
  margin: 18px 0 24px;
  max-width: 570px;
  font-size: 18px;
}
.intro-links {
  display: flex;
  align-items: center;
  gap: 24px;
}
.intro-links a {
  text-decoration: none;
  font-size: 15px;
}
.intro-links span {
  margin-left: 14px;
}
.primary {
  background: var(--blue);
  color: white;
  padding: 11px 18px;
  border-radius: 5px;
}
.primary:hover {
  background: #194974;
}
.section-nav {
  display: flex;
  gap: 30px;
  padding: 16px 0;
  border-block: 1px solid var(--line);
  font-size: 14px;
}
.section-nav a {
  color: var(--ink);
  text-decoration: none;
}
.section-nav a:hover {
  text-decoration: underline;
}
.example {
  padding: 42px 0 48px;
  border-bottom: 1px solid var(--line);
}
.section-head {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 20px;
  margin-bottom: 26px;
}
.section-head p {
  margin-top: 8px;
}
.annotation {
  font-size: 12px;
  color: var(--muted);
  white-space: nowrap;
  padding-top: 7px;
}
.toolbar {
  display: flex;
  align-items: center;
  gap: 30px;
  margin-bottom: 22px;
}
.toolbar p {
  font-size: 14px;
  max-width: 510px;
}
.toolbar fieldset {
  margin: 0;
  padding: 0;
  border: 0;
  flex-shrink: 0;
}
.toolbar legend {
  font-size: 12px;
  margin-bottom: 7px;
  color: var(--muted);
}
.segmented {
  display: flex;
  border: 1px solid var(--line);
  border-radius: 5px;
  overflow: hidden;
  background: white;
}
.segmented button {
  border: 0;
  padding: 7px 16px;
  background: transparent;
  color: var(--muted);
  font-size: 14px;
}
.segmented button[aria-pressed="true"] {
  background: var(--blue);
  color: white;
}
.system-map {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr;
  gap: 24px;
}
.lane {
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 20px;
  background: var(--white);
  position: relative;
  display: flex;
  flex-direction: column;
}
.lane:not(:last-child)::after {
  content: "→";
  position: absolute;
  right: -21px;
  top: 112px;
  font-size: 20px;
  color: var(--blue);
  z-index: 1;
}
.data-lane {
  background: var(--tint);
  border-color: #b6cde0;
}
.lane-heading {
  font-size: 14px;
  font-weight: 600;
  margin-bottom: 20px;
}
.lane-heading span {
  display: block;
  font-size: 12px;
  font-weight: 400;
  color: var(--muted);
  margin-top: 2px;
}
.node {
  display: flex;
  align-items: flex-start;
  gap: 12px;
  padding: 14px 10px;
  border: 1px solid var(--line);
  border-radius: 6px;
  background: white;
  min-height: 108px;
  transition:
    border-color 0.16s,
    background 0.16s;
}
.node svg {
  width: 28px;
  height: 28px;
  flex-shrink: 0;
  fill: none;
  stroke: var(--blue);
  stroke-width: 1.7;
  stroke-linecap: round;
  stroke-linejoin: round;
  margin-top: 2px;
}
.node p {
  font-size: 13px;
  margin-top: 2px;
}
.node code {
  font:
    12px/1.5 ui-monospace,
    SFMono-Regular,
    Consolas,
    monospace;
  display: block;
  margin-top: 10px;
  color: var(--ink);
  overflow-wrap: anywhere;
}
.node.active {
  border: 2px solid var(--blue);
  padding: 13px 9px;
  background: #f8fbff;
}
.node.active h3::after {
  content: " · current";
  font-weight: 400;
  color: var(--blue);
  font-size: 12px;
}
.connector {
  height: 56px;
  display: flex;
  gap: 10px;
  align-items: center;
  justify-content: center;
  font-size: 11px;
  color: var(--muted);
}
.connector i {
  height: 27px;
  width: 1px;
  background: var(--blue);
  position: relative;
}
.connector i::after {
  content: "";
  position: absolute;
  bottom: 0;
  left: -3px;
  border-top: 5px solid var(--blue);
  border-inline: 3.5px solid transparent;
}
.rule-node {
  border-style: dashed;
}
.access {
  font-size: 12px;
  margin-top: auto;
  padding-top: 20px;
}
.boundary-note {
  display: flex;
  gap: 12px;
  padding: 24px 2px;
  align-items: flex-start;
}
.boundary-note p {
  font-size: 14px;
}
.line-swatch {
  height: 20px;
  width: 20px;
  border: 1px dashed var(--muted);
  flex-shrink: 0;
  margin-top: 3px;
}
.trace {
  padding: 18px 0 12px;
  display: flex;
  gap: 22px;
  align-items: center;
}
.trace-controls {
  display: flex;
  gap: 8px;
  flex-shrink: 0;
}
.trace button {
  background: white;
  border: 1px solid var(--line);
  border-radius: 5px;
  padding: 7px 12px;
  font-size: 13px;
  color: var(--blue);
}
.trace button:hover {
  border-color: var(--blue);
}
.trace .quiet {
  background: transparent;
  color: var(--muted);
}
.trace p {
  font-size: 13px;
}
.map-key {
  font-size: 12px;
  max-width: 950px;
}
.calculator {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 60px;
}
.case-select label {
  display: block;
  font-size: 13px;
  color: var(--muted);
  margin-bottom: 8px;
}
select {
  width: 100%;
  max-width: 380px;
  background: white;
  border: 1px solid var(--line);
  border-radius: 5px;
  padding: 10px;
  color: var(--ink);
}
.case-select > p {
  font-size: 15px;
  margin: 16px 0 20px;
  max-width: 430px;
}
details {
  border-block: 1px solid var(--line);
  padding: 13px 0;
  max-width: 430px;
}
summary {
  cursor: pointer;
  font-size: 14px;
  color: var(--blue);
}
.rule-example p {
  font-size: 13px;
  margin-top: 14px;
}
.math {
  font-variant-numeric: tabular-nums;
}
.math > div {
  display: flex;
  justify-content: space-between;
  gap: 20px;
  padding: 11px 0;
  font-size: 15px;
}
.math output {
  font-weight: 500;
}
.math .subtotal {
  border-top: 1px solid var(--line);
}
.math .result {
  border-top: 1px solid var(--ink);
  margin-top: 5px;
  color: var(--blue);
  font-size: 18px;
}
.comparison {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 60px;
}
.comparison h3 {
  margin-bottom: 14px;
}
.comparison ol {
  list-style: none;
  padding: 0;
  margin: 0;
  counter-reset: step;
}
.comparison li {
  position: relative;
  margin-left: 12px;
  padding: 0 0 22px 26px;
  border-left: 1px solid var(--line);
  font-size: 15px;
  counter-increment: step;
}
.comparison li:last-child {
  border-left-color: transparent;
  padding-bottom: 8px;
}
.comparison li::before {
  content: counter(step);
  position: absolute;
  left: -12px;
  top: 0;
  width: 23px;
  height: 23px;
  background: var(--paper);
  border: 1px solid var(--line);
  border-radius: 50%;
  text-align: center;
  font-size: 12px;
  line-height: 22px;
}
.comparison li span {
  display: block;
  font-size: 12px;
  color: var(--muted);
}
.comparison li.machine::before {
  background: var(--tint);
  border-color: var(--blue);
  color: var(--blue);
}
.comparison li.machine span {
  color: var(--blue);
}
.comparison p {
  font-size: 14px;
  margin-top: 16px;
  max-width: 420px;
}
.method {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 60px;
  padding: 45px 0;
}
.method p {
  margin: 12px 0 20px;
  max-width: 440px;
}
.method > a,
.method a {
  font-size: 14px;
}
.method dl {
  margin: 0;
}
.method dl div {
  padding: 0 0 18px;
}
.method dt {
  font-size: 15px;
  font-weight: 500;
}
.method dd {
  margin: 3px 0 0;
  font-size: 14px;
  color: var(--muted);
}
footer {
  padding: 22px 0 30px;
  border-top: 1px solid var(--line);
  display: flex;
  justify-content: space-between;
  gap: 20px;
  font-size: 12px;
  color: var(--muted);
}
footer div {
  display: flex;
  gap: 20px;
}
footer a {
  text-decoration: none;
  color: var(--muted);
}
@media (max-width: 950px) {
  .system-map {
    gap: 18px;
  }
  .lane {
    padding: 14px;
  }
  .lane:not(:last-child)::after {
    right: -17px;
  }
  .node {
    gap: 7px;
  }
  .node svg {
    width: 22px;
  }
  .section-head {
    display: block;
  }
  .annotation {
    display: block;
    margin-top: 8px;
  }
  .trace {
    align-items: flex-start;
    flex-direction: column;
    gap: 10px;
  }
  .calculator,
  .comparison,
  .method {
    gap: 32px;
  }
}
@media (max-width: 700px) {
  .site-header {
    padding: 18px 20px;
    align-items: flex-start;
    gap: 16px;
  }
  .site-header nav {
    gap: 14px;
    font-size: 12px;
  }
  .site-header nav a:first-child {
    display: none;
  }
  .wordmark {
    font-size: 14px;
    gap: 7px;
  }
  .wordmark img {
    width: 22px;
    height: 22px;
  }
  main {
    padding: 0 20px;
  }
  .intro {
    padding: 38px 0 30px;
  }
  .intro p {
    font-size: 16px;
  }
  .section-nav {
    gap: 20px;
    flex-wrap: wrap;
    font-size: 12px;
  }
  .example {
    padding: 30px 0;
  }
  h2 {
    font-size: 22px;
  }
  .section-head p {
    font-size: 15px;
  }
  .annotation {
    white-space: normal;
  }
  .toolbar {
    align-items: flex-start;
    flex-direction: column;
    gap: 12px;
  }
  .system-map {
    grid-template-columns: 1fr;
    gap: 28px;
  }
  .lane {
    padding: 18px;
  }
  .lane:not(:last-child)::after {
    content: "↓";
    top: auto;
    right: 50%;
    bottom: -29px;
  }
  .node {
    min-height: 100px;
    gap: 14px;
    padding: 14px;
  }
  .node.active {
    padding: 13px;
  }
  .node svg {
    width: 28px;
  }
  .node p {
    font-size: 14px;
  }
  .node code {
    font-size: 13px;
  }
  .connector {
    font-size: 12px;
  }
  .lane-heading {
    margin-bottom: 14px;
  }
  .access {
    padding-top: 15px;
  }
  .boundary-note {
    padding: 20px 0 0;
  }
  .calculator,
  .comparison,
  .method {
    grid-template-columns: 1fr;
    gap: 28px;
  }
  .math {
    padding-top: 4px;
  }
  .comparison > div + div {
    padding-top: 12px;
  }
  .method {
    padding: 30px 0;
  }
  .trace-controls {
    flex-wrap: wrap;
  }
  .trace button {
    font-size: 12px;
  }
  footer {
    flex-direction: column;
  }
  footer div {
    flex-wrap: wrap;
    gap: 15px;
  }
  .intro-links {
    gap: 18px;
  }
}
@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }
  * {
    transition: none !important;
  }
}
@media print {
  .site-header nav,
  .intro-links,
  .section-nav,
  .trace-controls,
  footer {
    display: none;
  }
  body {
    background: white;
  }
  .example {
    break-inside: avoid;
  }
  .system-map {
    grid-template-columns: repeat(3, 1fr);
  }
  .lane:not(:last-child)::after {
    content: "→";
    right: -21px;
    top: 112px;
    bottom: auto;
  }
  details {
    display: block;
  }
  details > * {
    display: block;
  }
  .calculator,
  .comparison {
    grid-template-columns: 1fr 1fr;
  }
}

/* Edges connect actual nodes, independently of the ownership containers. */
.system-map {
  position: relative;
}
.flow-edges {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  z-index: 2;
  overflow: visible;
  pointer-events: none;
}
.flow-edges path.edge {
  fill: none;
  stroke: var(--blue);
  stroke-width: 1.5;
  marker-end: url(#arrow);
}
.lane:not(:last-child)::after {
  display: none;
}
.intro {
  padding-top: 38px;
  padding-bottom: 30px;
}
.intro h1 {
  font-size: 38px;
}
.intro p {
  margin: 12px 0 20px;
}
.node,
.lane-heading,
.access,
.connector,
.boundary-note {
  position: relative;
  z-index: 3;
}
.node {
  z-index: 4;
}
@media (max-width: 700px) {
  .flow-edges {
    display: none;
  }
  .lane:not(:last-child)::after {
    display: block;
  }
  .intro h1 {
    font-size: 32px;
  }
}