:root {
  color-scheme: light;

  /* OKLCH — canonical tokens aligned with Back Pro Ivory Editorial */
  --bp-bg: oklch(97.2% 0.008 85);
  --bp-bg-secondary: oklch(98.6% 0.006 85);
  --bp-card: oklch(100% 0 0);
  --bp-ink: oklch(22% 0.012 75);
  --bp-ink-secondary: oklch(46% 0.018 75);
  --bp-ink-muted: oklch(52% 0.014 75);
  --bp-accent: oklch(72% 0.09 78);
  --bp-accent-pressed: oklch(58% 0.1 72);
  --bp-accent-soft: oklch(92% 0.035 82);
  --bp-accent-glow: oklch(88% 0.06 80);
  --bp-border: oklch(90% 0.012 82);
  --bp-focus: oklch(68% 0.11 78);

  --max-width: 44rem;
  --radius-sm: 10px;
  --radius-md: 12px;
  --radius-card: 16px;
  --radius-pill: 999px;

  --space-xs: 0.5rem;
  --space-sm: 0.75rem;
  --space-md: 1rem;
  --space-lg: 1.5rem;
  --space-xl: 2rem;
  --space-2xl: 2.5rem;

  --ease-out: cubic-bezier(0.22, 1, 0.36, 1);
  --dur-fast: 160ms;
  --dur-normal: 220ms;

  --header-height: 4.5rem;
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
}

body {
  margin: 0;
  min-height: 100vh;
  background: var(--bp-bg);
  color: var(--bp-ink);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue",
    Arial, "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  font-size: 1rem;
  line-height: 1.65;
  position: relative;
}

body::before {
  content: "";
  position: fixed;
  inset: 0;
  pointer-events: none;
  z-index: -1;
  background:
    radial-gradient(ellipse 80% 50% at 100% -10%, oklch(94% 0.04 82 / 0.55), transparent 55%),
    radial-gradient(ellipse 60% 40% at -5% 100%, oklch(95% 0.03 78 / 0.4), transparent 50%),
    linear-gradient(180deg, var(--bp-bg-secondary), var(--bp-bg));
}

a {
  color: var(--bp-accent-pressed);
  text-decoration-thickness: 1px;
  text-underline-offset: 0.15em;
  transition: color var(--dur-fast) var(--ease-out);
}

a:hover {
  color: var(--bp-accent);
  text-decoration: underline;
}

.skip-link {
  position: absolute;
  left: var(--space-md);
  top: -100%;
  z-index: 1000;
  padding: 0.625rem 1rem;
  border-radius: var(--radius-md);
  background: var(--bp-ink);
  color: var(--bp-card);
  font-weight: 700;
  font-size: 0.875rem;
  text-decoration: none;
  transition: top var(--dur-fast) var(--ease-out);
}

.skip-link:focus {
  top: var(--space-md);
  outline: 2px solid var(--bp-focus);
  outline-offset: 2px;
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  border-bottom: 1px solid oklch(88% 0.012 82 / 0.65);
  background: oklch(99% 0.004 85 / 0.82);
  backdrop-filter: blur(12px) saturate(1.1);
  -webkit-backdrop-filter: blur(12px) saturate(1.1);
}

.site-header-inner,
.page-inner,
.site-footer-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: var(--space-lg) var(--space-xl);
}

.site-brand {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  text-decoration: none;
  color: var(--bp-ink);
  transition: opacity var(--dur-fast) var(--ease-out);
}

.site-brand:hover {
  opacity: 0.88;
  text-decoration: none;
}

.site-brand:focus-visible {
  outline: 2px solid var(--bp-focus);
  outline-offset: 4px;
  border-radius: var(--radius-sm);
}

.site-brand img {
  width: 2.5rem;
  height: 2.5rem;
  border-radius: var(--radius-sm);
  box-shadow: 0 0 0 1px oklch(80% 0.02 75 / 0.25);
}

.site-brand-title {
  font-size: 1.125rem;
  font-weight: 800;
  letter-spacing: -0.03em;
}

.site-brand-subtitle {
  display: block;
  font-size: 0.8125rem;
  font-weight: 500;
  color: var(--bp-ink-secondary);
  margin-top: 0.125rem;
}

.site-nav {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-sm) var(--space-md);
  margin-top: var(--space-md);
}

.site-links {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-xs) var(--space-lg);
}

.site-links a {
  position: relative;
  color: var(--bp-ink-secondary);
  font-size: 0.9375rem;
  font-weight: 600;
  text-decoration: none;
  padding: 0.375rem 0;
  min-height: 2.75rem;
  display: inline-flex;
  align-items: center;
}

.site-links a::after {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0.25rem;
  height: 2px;
  border-radius: 1px;
  background: var(--bp-accent);
  transform: scaleX(0);
  transform-origin: left;
  transition: transform var(--dur-normal) var(--ease-out);
}

.site-links a:hover {
  color: var(--bp-ink);
  text-decoration: none;
}

.site-links a:hover::after,
.site-links a.is-active::after {
  transform: scaleX(1);
}

.site-links a.is-active {
  color: var(--bp-ink);
}

.site-links a:focus-visible {
  outline: 2px solid var(--bp-focus);
  outline-offset: 4px;
  border-radius: 4px;
}

.lang-toggle {
  display: inline-flex;
  border: 1px solid var(--bp-border);
  border-radius: var(--radius-pill);
  overflow: hidden;
  background: var(--bp-card);
  padding: 2px;
}

.lang-toggle button {
  border: 0;
  background: transparent;
  color: var(--bp-ink-secondary);
  font: inherit;
  font-size: 0.8125rem;
  font-weight: 700;
  padding: 0.4375rem 0.875rem;
  min-height: 2.75rem;
  min-width: 2.75rem;
  cursor: pointer;
  border-radius: var(--radius-pill);
  transition:
    background var(--dur-fast) var(--ease-out),
    color var(--dur-fast) var(--ease-out),
    transform var(--dur-fast) var(--ease-out);
}

.lang-toggle button:hover {
  color: var(--bp-ink);
}

.lang-toggle button.is-active {
  background: linear-gradient(
    180deg,
    oklch(94% 0.04 82),
    oklch(91% 0.045 80)
  );
  color: var(--bp-ink);
  box-shadow: inset 0 1px 0 oklch(100% 0 0 / 0.6);
}

.lang-toggle button:focus-visible {
  outline: 2px solid var(--bp-focus);
  outline-offset: 1px;
}

.lang-toggle button:active {
  transform: scale(0.97);
}

.page-main {
  padding: var(--space-xl) 0 var(--space-2xl);
}

.page-kicker {
  display: inline-block;
  margin-bottom: var(--space-sm);
  padding: 0.25rem 0.625rem;
  border-radius: var(--radius-pill);
  background: oklch(94% 0.03 82);
  border: 1px solid var(--bp-border);
  color: var(--bp-ink-secondary);
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: 0.04em;
  text-transform: uppercase;
}

.hero-card,
.content-card,
.nav-card {
  background: var(--bp-card);
  border: 1px solid var(--bp-border);
  border-radius: var(--radius-card);
  padding: var(--space-xl);
  margin-bottom: var(--space-md);
}

.hero-card,
.content-card,
.nav-card {
  animation: fade-rise var(--dur-normal) var(--ease-out) both;
}

.nav-grid .nav-card:nth-child(1) {
  animation-delay: 80ms;
}

.nav-grid .nav-card:nth-child(2) {
  animation-delay: 140ms;
}

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

.hero-card h1,
.content-card h1 {
  margin: 0 0 var(--space-sm);
  font-size: clamp(1.75rem, 4vw, 2.125rem);
  line-height: 1.2;
  letter-spacing: -0.03em;
  text-wrap: balance;
  max-width: 20ch;
}

.lead {
  margin: 0;
  color: var(--bp-ink-secondary);
  font-size: 1.0625rem;
  text-wrap: pretty;
  max-width: 42rem;
}

.meta {
  margin-top: var(--space-sm);
  color: var(--bp-ink-muted);
  font-size: 0.875rem;
}

.content-card {
  max-width: 100%;
}

.content-card h2 {
  margin: var(--space-xl) 0 var(--space-sm);
  font-size: 1.0625rem;
  line-height: 1.35;
  letter-spacing: -0.02em;
  color: var(--bp-ink);
  text-wrap: balance;
}

.content-card h2:first-child {
  margin-top: 0;
}

.content-card p,
.content-card li {
  color: var(--bp-ink-secondary);
  text-wrap: pretty;
  max-width: 42rem;
}

.content-card ul,
.content-card ol {
  margin: var(--space-sm) 0 0;
  padding-left: 1.25rem;
}

.content-card li + li {
  margin-top: 0.375rem;
}

.content-card code {
  padding: 0.125rem 0.375rem;
  border-radius: 6px;
  background: oklch(95% 0.02 82);
  border: 1px solid var(--bp-border);
  font-size: 0.875em;
  color: var(--bp-ink);
}

.nav-grid {
  display: grid;
  gap: var(--space-sm);
}

.nav-card {
  display: block;
  color: inherit;
  text-decoration: none;
  transition:
    border-color var(--dur-normal) var(--ease-out),
    transform var(--dur-normal) var(--ease-out),
    background var(--dur-normal) var(--ease-out);
}

.nav-card:hover {
  border-color: oklch(78% 0.08 78);
  background: oklch(99.5% 0.008 85);
  transform: translateY(-2px);
  text-decoration: none;
}

.nav-card:focus-visible {
  outline: 2px solid var(--bp-focus);
  outline-offset: 3px;
}

.nav-card-title {
  font-size: 1.0625rem;
  font-weight: 800;
  margin-bottom: 0.375rem;
  letter-spacing: -0.02em;
}

.nav-card-desc {
  color: var(--bp-ink-secondary);
  font-size: 0.9375rem;
}

.nav-card-arrow {
  display: inline-block;
  margin-top: var(--space-sm);
  color: var(--bp-accent-pressed);
  font-size: 0.875rem;
  font-weight: 700;
  transition: transform var(--dur-fast) var(--ease-out);
}

.nav-card:hover .nav-card-arrow {
  transform: translateX(3px);
}

.faq-item + .faq-item {
  margin-top: var(--space-lg);
  padding-top: var(--space-lg);
  border-top: 1px solid var(--bp-border);
}

.faq-q {
  margin: 0 0 var(--space-sm);
  font-size: 1rem;
  font-weight: 800;
  color: var(--bp-ink);
  letter-spacing: -0.02em;
}

.faq-a {
  margin: 0;
  color: var(--bp-ink-secondary);
}

.contact-box {
  margin-top: var(--space-sm);
  padding: var(--space-md);
  border-radius: var(--radius-md);
  background: linear-gradient(
    145deg,
    oklch(94% 0.04 82),
    oklch(91% 0.045 80)
  );
  border: 1px solid oklch(84% 0.04 80);
}

.contact-box a {
  font-weight: 700;
}

.site-footer {
  border-top: 1px solid var(--bp-border);
  color: var(--bp-ink-muted);
  font-size: 0.875rem;
  background: oklch(98.8% 0.005 85 / 0.6);
}

.site-footer-inner {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  align-items: center;
  gap: var(--space-sm) var(--space-md);
}

.site-footer a {
  font-weight: 600;
}

:not(html)[lang="zh"],
:not(html)[lang="en"] {
  display: none;
}

html[data-lang="zh"] :not(html)[lang="zh"],
html[data-lang="en"] :not(html)[lang="en"] {
  display: revert;
}

@media (max-width: 600px) {
  .site-header-inner,
  .page-inner,
  .site-footer-inner {
    padding-left: var(--space-md);
    padding-right: var(--space-md);
  }

  .hero-card,
  .content-card,
  .nav-card {
    padding: var(--space-lg) var(--space-md);
  }

  .hero-card h1,
  .content-card h1 {
    max-width: none;
  }
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }

  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }

  .nav-card:hover {
    transform: none;
  }
}