@import url('https://fonts.googleapis.com/css2?family=Chakra+Petch:wght@500;600&family=Inter:wght@400;500&display=swap');

:root {
  --navy-900: #0F2440;
  --navy-700: #1B3F72;
  --blue-500: #2459A0;
  --blue-300: #6DB8FF;
  --blue-100: #EAF3FF;
  --paper: #F7F9FC;
  --ink: #16223A;
  --ink-soft: #4A6FA5;
  --hairline: #D8E4F2;
  --card-bg: #FFFFFF;
  --block-a: #2459A0;
  --block-b: #1B3F72;
  --max-w: 640px;
  --radius: 6px;
}

html[data-theme="dark"] {
  --navy-900: #EAF3FF;
  --navy-700: #BFE0FF;
  --blue-500: #6DB8FF;
  --blue-300: #6DB8FF;
  --blue-100: #142A47;
  --paper: #0B1526;
  --ink: #DCE6F5;
  --ink-soft: #8CA3C4;
  --hairline: #23324A;
  --card-bg: #101F36;
  --block-a: #3E7FCB;
  --block-b: #2C5A96;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: 'Inter', system-ui, sans-serif;
  font-size: 16px;
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
  transition: background-color 0.15s ease, color 0.15s ease;
}

a { color: var(--blue-500); text-decoration: none; }
a:hover { color: var(--navy-900); text-decoration: underline; }
a:focus-visible, button:focus-visible {
  outline: 2px solid var(--blue-300);
  outline-offset: 3px;
}

.brand-mark {
  font-family: 'Chakra Petch', sans-serif;
  font-weight: 600;
  font-size: 20px;
  color: var(--navy-900);
  letter-spacing: 0.3px;
  display: inline-flex;
  align-items: baseline;
  gap: 2px;
}
.brand-mark:hover { text-decoration: none; color: var(--navy-900); }

header {
  border-bottom: 1px solid var(--hairline);
}

.header-inner {
  max-width: 920px;
  margin: 0 auto;
  padding: 22px 32px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
  flex-wrap: wrap;
}

.nav-wrap {
  display: flex;
  align-items: center;
  gap: 24px;
  flex-wrap: wrap;
}

nav.menu {
  display: flex;
  gap: 28px;
  font-size: 15px;
}

nav.menu a {
  color: var(--ink-soft);
}
nav.menu a:hover { color: var(--navy-900); }

.site-toggles {
  display: flex;
  align-items: center;
  gap: 8px;
}

.toggle-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  height: 30px;
  padding: 0 10px;
  border: 1px solid var(--hairline);
  border-radius: var(--radius);
  background: transparent;
  color: var(--ink-soft);
  font-family: 'Inter', system-ui, sans-serif;
  font-size: 13px;
  font-weight: 500;
  cursor: pointer;
  text-decoration: none;
  line-height: 1;
}
.toggle-btn:hover { color: var(--navy-900); border-color: var(--navy-700); text-decoration: none; }
.toggle-btn.icon-btn { width: 30px; padding: 0; }

.theme-toggle svg { width: 16px; height: 16px; display: none; color: inherit; }
html[data-theme="light"] .theme-toggle .icon-moon { display: block; }
html[data-theme="dark"] .theme-toggle .icon-sun { display: block; }

main {
  max-width: 920px;
  margin: 0 auto;
  padding: 0 32px;
}

.hero {
  padding: 96px 0 64px;
  text-align: center;
}

.hero-logo { max-width: 460px; width: 100%; height: auto; margin: 0 auto; display: block; }
.hero-logo .logo-fill { fill: var(--navy-900); }
.hero-logo .qkv-a { fill: var(--block-a); }
.hero-logo .qkv-b { fill: var(--block-b); }

.tagline {
  margin-top: 22px;
  font-family: 'Chakra Petch', sans-serif;
  font-weight: 400;
  font-size: 14px;
  letter-spacing: 2px;
  color: var(--ink-soft);
}

.copy {
  max-width: var(--max-w);
  margin: 0 auto;
  padding-bottom: 96px;
}

.copy h2 {
  font-family: 'Chakra Petch', sans-serif;
  font-weight: 500;
  font-size: 18px;
  color: var(--navy-900);
  margin: 40px 0 12px;
}

.copy p { margin: 0 0 16px; color: var(--ink); }
.copy p:first-of-type { margin-top: 0; }

.signature {
  margin-top: 32px;
  font-family: 'Chakra Petch', sans-serif;
  font-weight: 500;
  font-size: 15px;
  letter-spacing: 0.5px;
  color: var(--navy-900);
}

.page-title {
  font-family: 'Chakra Petch', sans-serif;
  font-weight: 600;
  font-size: 30px;
  color: var(--navy-900);
  margin: 56px 0 8px;
}

.page-lede {
  color: var(--ink-soft);
  max-width: var(--max-w);
  margin: 0 0 40px;
}

.logo-figure {
  background: var(--card-bg);
  border: 1px solid var(--hairline);
  border-radius: 12px;
  padding: 48px 32px;
  margin-bottom: 48px;
}

.logo-figure svg { max-width: 520px; width: 100%; height: auto; display: block; margin: 0 auto; }
.logo-figure .logo-fill { fill: var(--navy-900); }
.logo-figure .qkv-a { fill: var(--block-a); }
.logo-figure .qkv-b { fill: var(--block-b); }

.explainer { max-width: var(--max-w); padding-bottom: 96px; }

.explainer h2 {
  font-family: 'Chakra Petch', sans-serif;
  font-weight: 500;
  font-size: 18px;
  color: var(--navy-900);
  margin: 36px 0 10px;
}

.explainer p { margin: 0 0 16px; }
.explainer p:first-child { margin-top: 0; }

.explainer code {
  font-family: 'Chakra Petch', sans-serif;
  background: var(--blue-100);
  color: var(--navy-700);
  padding: 1px 6px;
  border-radius: 4px;
  font-size: 14px;
}

.explainer h3 {
  font-family: 'Chakra Petch', sans-serif;
  font-weight: 500;
  font-size: 15px;
  color: var(--navy-700);
  margin: 28px 0 6px;
}
.explainer h3:first-of-type { margin-top: 0; }

.explainer .source-note {
  font-size: 14px;
  color: var(--ink-soft);
}

footer {
  border-top: 1px solid var(--hairline);
  padding: 28px 32px;
  text-align: center;
  color: var(--ink-soft);
  font-size: 13px;
}

@media (max-width: 640px) {
  .header-inner { padding: 18px 20px; }
  main { padding: 0 20px; }
  nav.menu { gap: 18px; font-size: 14px; }
  .nav-wrap { gap: 16px; }
  .hero { padding: 64px 0 48px; }
  .page-title { font-size: 26px; }
}