:root {
  color-scheme: light;
  --ink: #101828;
  --muted: #536174;
  --paper: #f7f8fa;
  --card: #fff;
  --line: #c9d0db;
  --blue: #1859d1;
  --blue-soft: #e8efff;
  --red: #b42318;
  --red-soft: #fff0ee;
  --amber: #8a4b08;
  --amber-soft: #fff4df;
  --code: #0b1220;
  --signal: #ff5c35;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  background-color: var(--paper);
  background-image:
    linear-gradient(rgba(16, 24, 40, 0.035) 1px, transparent 1px),
    linear-gradient(90deg, rgba(16, 24, 40, 0.035) 1px, transparent 1px);
  background-size: 32px 32px;
  color: var(--ink);
  font-family: Arial, Helvetica, sans-serif;
  line-height: 1.6;
}

a {
  color: var(--blue);
  text-underline-offset: 3px;
}

.site-header,
.site-footer,
main {
  width: min(1180px, calc(100% - 40px));
  margin: 0 auto;
}

.site-header {
  display: flex;
  min-height: 76px;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
  padding: 0;
  border-bottom: 1px solid var(--ink);
}

.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  color: var(--ink);
  font: 800 1.03rem/1 ui-monospace, SFMono-Regular, Menlo, monospace;
  letter-spacing: -0.04em;
  text-decoration: none;
}

.mark {
  display: grid;
  width: 22px;
  height: 22px;
  place-items: center;
  background: var(--signal);
}

.mark::after {
  content: "F";
  color: #fff;
  font: 800 13px/1 ui-monospace, SFMono-Regular, Menlo, monospace;
}

.nav {
  display: flex;
  align-items: center;
}

.nav a {
  padding: 28px 13px 25px;
  border-bottom: 3px solid transparent;
  color: var(--ink);
  font-size: 0.86rem;
  font-weight: 650;
  text-decoration: none;
}

.nav a:hover,
.nav a[aria-current="page"] {
  border-bottom-color: var(--signal);
  color: var(--ink);
}

main {
  padding: 0 0 96px;
}

h1 {
  max-width: 900px;
  margin: 0 0 20px;
  font-size: clamp(2.5rem, 6vw, 5.8rem);
  letter-spacing: -0.065em;
  line-height: 0.94;
}

h2 {
  margin: 0 0 13px;
  font-size: clamp(1.45rem, 3vw, 2rem);
  letter-spacing: -0.045em;
  line-height: 1.18;
}

h3 {
  letter-spacing: -0.025em;
  line-height: 1.25;
}

.lead {
  max-width: 760px;
  margin: 0;
  color: var(--muted);
  font-size: clamp(1.08rem, 2vw, 1.28rem);
  line-height: 1.55;
}

.hero {
  padding: 80px 0 52px;
}

.hero.home {
  display: grid;
  grid-template-columns: minmax(0, 1.05fr) minmax(340px, 0.95fr);
  align-items: center;
  gap: 70px;
  padding: 76px 0 64px;
}

.actions {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin-top: 30px;
}

button,
.button {
  display: inline-block;
  padding: 13px 17px;
  border: 1px solid var(--ink);
  border-radius: 2px;
  background: var(--ink);
  color: #fff;
  cursor: pointer;
  font: inherit;
  font-size: 0.94rem;
  font-weight: 720;
  text-decoration: none;
}

button:hover,
.button:hover {
  border-color: var(--signal);
  background: var(--signal);
  color: #fff;
}

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

.button.secondary:hover {
  background: var(--ink);
  color: #fff;
}

.protocol-map {
  border: 1px solid var(--ink);
  background: var(--card);
  box-shadow: 10px 10px 0 var(--ink);
  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
}

.protocol-map > div {
  display: grid;
  grid-template-columns: 46px 1fr;
  gap: 2px 12px;
  padding: 14px 16px;
}

.protocol-map span {
  grid-row: 1 / 3;
  color: var(--signal);
  font-size: 0.73rem;
}

.protocol-map strong {
  font-size: 0.9rem;
}

.protocol-map small,
.protocol-map code {
  color: var(--muted);
  font-size: 0.76rem;
}

.protocol-in,
.protocol-out {
  background: #f0f3f8;
}

.section {
  padding: 58px 0;
}

.section-head {
  max-width: 760px;
  margin-bottom: 30px;
}

.section-head p,
.card p,
.article p,
.article li {
  color: var(--muted);
}

.grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  border-top: 1px solid var(--ink);
  border-left: 1px solid var(--line);
}

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

.card {
  padding: 28px;
  border: 0;
  border-right: 1px solid var(--line);
  background: rgba(255, 255, 255, 0.72);
}

.card h2,
.card h3,
.article-section h2 {
  margin-top: 0;
}

.card p:last-child,
.article-section p:last-child {
  margin-bottom: 0;
}

.steps {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  margin: 0;
  padding: 0;
  border-top: 1px solid var(--ink);
  border-left: 1px solid var(--line);
  counter-reset: step;
  list-style: none;
}

.steps li {
  padding: 25px;
  border-right: 1px solid var(--line);
  background: rgba(255, 255, 255, 0.72);
  color: var(--muted);
}

.steps li::before {
  display: block;
  margin-bottom: 8px;
  color: var(--signal);
  content: counter(step);
  counter-increment: step;
  font: 700 0.78rem ui-monospace, SFMono-Regular, Menlo, monospace;
}

.lookup {
  display: flex;
  max-width: 760px;
  margin: 30px 0 18px;
}

.lookup input {
  min-width: 0;
  flex: 1;
  padding: 16px 17px;
  border: 1px solid var(--ink);
  border-radius: 2px;
  background: var(--card);
  font: inherit;
  font-size: 1.08rem;
}

.lookup button {
  border-left: 0;
}

.lookup input:focus,
textarea:focus {
  border-color: var(--blue);
  outline: 3px solid rgba(24, 89, 209, 0.22);
}

.visually-hidden {
  position: absolute;
  left: -10000px;
}

.hint {
  color: var(--muted);
  font-size: 0.88rem;
}

.test-mode {
  max-width: 760px;
  margin: 24px 0 0;
  padding: 12px 14px;
  border-left: 4px solid var(--signal);
  background: #fff2ed;
}

.tutorial-goal {
  max-width: 860px;
  margin: 32px 0 8px;
  padding: 28px 30px;
  border: 1px solid var(--ink);
  border-left: 6px solid var(--signal);
  background: #eef3ff;
}

.tutorial-goal ol {
  margin: 18px 0;
  padding-left: 24px;
}

.tutorial-goal p:last-child {
  margin-bottom: 0;
}

.expected-result {
  margin-top: 24px;
  padding-top: 22px;
  border-top: 1px dashed var(--line);
}

.expected-result > h3 {
  margin: 0 0 8px;
  font-size: 1rem;
}

.result {
  max-width: 760px;
  margin-top: 30px;
  padding: 28px;
  border: 1px solid var(--ink);
  background: var(--card);
  box-shadow: 8px 8px 0 #dce2ea;
}

.status {
  display: flex;
  align-items: flex-start;
  gap: 13px;
}

.icon {
  display: grid;
  width: 32px;
  height: 32px;
  flex: 0 0 auto;
  place-items: center;
  border-radius: 2px;
  font-weight: 800;
}

.capable .icon {
  background: var(--blue-soft);
  color: var(--blue);
}

.not-capable .icon,
.not-found .icon {
  background: var(--red-soft);
  color: var(--red);
}

.unavailable .icon,
.invalid .icon {
  background: var(--amber-soft);
  color: var(--amber);
}

.status h2 {
  margin: 2px 0 5px;
  font-size: 1.35rem;
}

.status p {
  margin: 0;
}

.facts {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 18px;
  margin-top: 22px;
  padding-top: 20px;
  border-top: 1px solid var(--line);
}

.fact small {
  display: block;
  margin-bottom: 3px;
  color: var(--muted);
}

.fact strong {
  font-size: 0.98rem;
}

.meta {
  margin-top: 20px;
  color: var(--muted);
  font-size: 0.78rem;
}

.cta {
  margin-top: 24px;
  padding-top: 22px;
  border-top: 1px solid var(--line);
}

.cta h3 {
  margin: 0 0 5px;
  font-size: 1.08rem;
}

.cta p {
  margin: 0 0 15px;
}

.callout {
  margin-top: 34px;
  padding: 28px;
  border: 1px solid var(--ink);
  border-left: 6px solid var(--signal);
  background: #eef3ff;
}

.callout h2 {
  margin-top: 0;
}

.code {
  display: block;
  overflow: auto;
  padding: 17px 18px;
  border-radius: 2px;
  background: var(--code);
  color: #eaf6ef;
  font: 13px/1.65 ui-monospace, SFMono-Regular, Menlo, monospace;
  white-space: pre;
}

.code-block {
  position: relative;
  margin: 1em 0;
}

.code-block .code {
  margin: 0;
  padding-right: 60px;
}

.copy-button {
  position: absolute;
  z-index: 1;
  top: 10px;
  right: 10px;
  display: grid;
  width: 36px;
  height: 36px;
  place-items: center;
  padding: 0;
  border: 1px solid #526078;
  border-radius: 2px;
  background: #172238;
  color: #fff;
}

.copy-button[hidden] {
  display: none;
}

.copy-button:hover,
.copy-button:focus-visible {
  border-color: var(--signal);
  background: var(--signal);
}

.copy-button.copied {
  border-color: #3da66b;
  background: #176b3a;
}

.copy-button svg {
  width: 17px;
  height: 17px;
  fill: none;
  stroke: currentColor;
  stroke-linecap: round;
  stroke-linejoin: round;
  stroke-width: 1.8;
}

.endpoint {
  display: grid;
  grid-template-columns: 190px 1fr;
  gap: 20px;
  padding: 18px 0;
  border-top: 1px solid var(--line);
}

.endpoint:first-child {
  border-top: 0;
}

.method,
.rule-id {
  color: var(--blue);
  font: 700 0.85rem ui-monospace, SFMono-Regular, Menlo, monospace;
}

.rule-id {
  font-size: 0.75rem;
}

.article {
  max-width: 860px;
}

.article .hero {
  padding-bottom: 24px;
}

.article-section {
  margin-top: 24px;
  padding: 26px 30px;
  border-left: 3px solid var(--line);
  background: rgba(255, 255, 255, 0.62);
}

.article-section:hover {
  border-left-color: var(--signal);
}

.article-section ul,
.article-section ol {
  padding-left: 22px;
}

.article-nav {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin-top: 34px;
}

.kicker {
  padding-bottom: 18px;
  color: var(--muted);
  font: 0.88rem ui-monospace, SFMono-Regular, Menlo, monospace;
}

textarea#xml {
  display: block;
  width: min(100%, 900px);
  margin-top: 10px;
  padding: 16px;
  border: 1px solid var(--ink);
  border-radius: 2px;
  background: #fff;
  font: 13px/1.55 ui-monospace, SFMono-Regular, Menlo, monospace;
}

.example-choices {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px 14px;
  margin: 26px 0 18px;
  font-size: 0.9rem;
}

.example-choices span {
  font-weight: 700;
}

.example-choices a {
  padding: 6px 10px;
  border: 1px solid var(--line);
  background: #fff;
  text-decoration: none;
}

.example-choices a:hover {
  border-color: var(--blue);
}

.site-footer {
  display: flex;
  justify-content: space-between;
  gap: 24px;
  padding: 28px 0 48px;
  border-top: 1px solid var(--ink);
  color: var(--muted);
  font-size: 0.88rem;
}

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

.footer-links a {
  color: var(--muted);
}

@media (max-width: 850px) {
  .hero.home {
    grid-template-columns: 1fr;
    gap: 40px;
  }

  .protocol-map {
    max-width: 640px;
  }

  .site-header {
    padding: 14px 0;
  }

  .nav {
    flex-wrap: wrap;
    justify-content: flex-end;
  }

  .nav a {
    padding: 10px 8px;
  }

  .grid,
  .grid.two,
  .steps {
    grid-template-columns: 1fr 1fr;
  }
}

@media (max-width: 600px) {
  .site-header,
  .site-footer,
  main {
    width: min(100% - 24px, 1180px);
  }

  .site-header {
    display: block;
  }

  .nav {
    justify-content: flex-start;
    margin-top: 12px;
  }

  .hero,
  .hero.home {
    padding-top: 48px;
  }

  .grid,
  .grid.two,
  .steps {
    grid-template-columns: 1fr;
  }

  .lookup {
    flex-direction: column;
  }

  .lookup button {
    width: 100%;
    border-top: 0;
    border-left: 1px solid var(--ink);
  }

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

  .protocol-map {
    box-shadow: 6px 6px 0 var(--ink);
  }

  h1 {
    font-size: clamp(2.55rem, 15vw, 4rem);
  }

  .site-footer {
    display: block;
  }

  .footer-links {
    margin-top: 14px;
  }
}