:root {
  --bg: #f4f6f9;
  --ink: #1e2430;
  --muted: #5a6478;
  --accent: #3a6ea5;
  --accent-soft: #5b8fc7;
  --accent-wash: #d9eaf4;
  --line: color-mix(in srgb, var(--accent) 18%, transparent);
  --surface: #ffffff;
  --font-display: "Fraunces", "Songti SC", "Noto Serif SC", serif;
  --font-body: "SimSun", "Songti SC", "STSong", "Noto Serif SC", serif;
  --font-flow: "Outfit", "DM Sans", "PingFang SC", sans-serif;
  --header-h: 64px;
  --radius: 4px;
  --ease: cubic-bezier(0.22, 1, 0.36, 1);
}

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

html {
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--header-h) + 12px);
}

body {
  margin: 0;
  font-family: var(--font-body);
  font-size: 16px;
  line-height: 1.65;
  color: var(--ink);
  background: var(--bg);
  -webkit-font-smoothing: antialiased;
}

a {
  color: var(--accent);
  text-decoration-thickness: 1px;
  text-underline-offset: 3px;
}

code,
pre {
  font-family: ui-monospace, "Cascadia Code", "SF Mono", Consolas, monospace;
  font-size: 0.9em;
}

code {
  padding: 0.12em 0.35em;
  border-radius: 3px;
  background: var(--accent-wash);
  color: var(--ink);
}

pre {
  margin: 0.75rem 0;
  padding: 0.9rem 1rem;
  overflow-x: auto;
  border-radius: var(--radius);
  background: #e8eef5;
  border: 1px solid var(--line);
}

.bg-glow {
  position: fixed;
  inset: 0;
  z-index: -1;
  pointer-events: none;
  background:
    radial-gradient(ellipse 80% 50% at 15% -10%, color-mix(in srgb, var(--accent-wash) 90%, transparent), transparent 55%),
    radial-gradient(ellipse 60% 40% at 90% 10%, color-mix(in srgb, var(--accent-soft) 22%, transparent), transparent 50%),
    linear-gradient(180deg, #eef3f8 0%, var(--bg) 42%, var(--bg) 100%);
}

/* Header */
.site-header {
  position: sticky;
  top: 0;
  z-index: 40;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  height: var(--header-h);
  padding: 0 clamp(1rem, 4vw, 2.5rem);
  background: color-mix(in srgb, var(--bg) 82%, transparent);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid transparent;
  transition: border-color 0.3s var(--ease), box-shadow 0.3s var(--ease);
}

.site-header.scrolled {
  border-bottom-color: var(--line);
  box-shadow: 0 8px 24px color-mix(in srgb, var(--ink) 4%, transparent);
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 0.55rem;
  color: var(--ink);
  text-decoration: none;
  font-weight: 700;
  font-size: 1.05rem;
  letter-spacing: -0.02em;
}

.brand img {
  display: block;
}

.nav {
  display: flex;
  align-items: center;
  gap: 0.25rem;
}

.nav a {
  position: relative;
  padding: 0.45rem 0.9rem;
  color: var(--muted);
  text-decoration: none;
  font-weight: 500;
  font-size: 0.95rem;
  border-radius: var(--radius);
  transition: color 0.2s var(--ease), background 0.2s var(--ease);
}

.nav a:hover {
  color: var(--accent);
  background: color-mix(in srgb, var(--accent-wash) 55%, transparent);
}

.nav a.active {
  color: var(--accent);
  background: var(--accent-wash);
}

.nav-toggle {
  display: none;
  flex-direction: column;
  justify-content: center;
  gap: 6px;
  width: 40px;
  height: 40px;
  padding: 0;
  border: none;
  background: transparent;
  cursor: pointer;
}

.nav-toggle span {
  display: block;
  width: 22px;
  height: 2px;
  margin-inline: auto;
  background: var(--ink);
  transition: transform 0.25s var(--ease), opacity 0.2s;
}

.nav-toggle[aria-expanded="true"] span:first-child {
  transform: translateY(4px) rotate(45deg);
}

.nav-toggle[aria-expanded="true"] span:last-child {
  transform: translateY(-4px) rotate(-45deg);
}

/* Sections */
.section {
  padding: clamp(3rem, 8vw, 5.5rem) clamp(1rem, 4vw, 2.5rem);
  max-width: 1100px;
  margin-inline: auto;
}

.section-head {
  margin-bottom: 2rem;
}

.section-head h2 {
  margin: 0 0 0.4rem;
  font-family: var(--font-display);
  font-size: clamp(1.75rem, 3.5vw, 2.35rem);
  font-weight: 700;
  letter-spacing: -0.02em;
}

.section-head p {
  margin: 0;
  color: var(--muted);
  max-width: 36rem;
}

/* Hero */
.hero {
  padding-top: clamp(2.5rem, 6vw, 4rem);
  min-height: calc(100svh - var(--header-h));
  display: flex;
  flex-direction: column;
  justify-content: center;
}

.hero-inner {
  text-align: center;
  max-width: 40rem;
  margin-inline: auto;
}

.hero-mark {
  display: block;
  width: clamp(3.5rem, 8vw, 4.25rem);
  height: clamp(3.5rem, 8vw, 4.25rem);
  margin: 0 auto 0.85rem;
  filter: drop-shadow(0 8px 20px color-mix(in srgb, var(--accent) 28%, transparent));
}

.hero-mark.reveal.in {
  animation: hero-mark-float 4.5s ease-in-out infinite;
}

.hero-title {
  margin: 0 0 0.75rem;
  font-family: var(--font-display);
  font-size: clamp(2.75rem, 8vw, 4.25rem);
  font-weight: 700;
  letter-spacing: -0.03em;
  line-height: 1.05;
  color: var(--ink);
}

.hero-lead {
  margin: 0 auto 1.75rem;
  color: var(--muted);
  font-size: clamp(1.1rem, 2.2vw, 1.25rem);
  line-height: 1.6;
}

/* Flow chain */
.flow-chain {
  display: flex;
  align-items: center;
  justify-content: center;
  flex-wrap: wrap;
  gap: 0.35rem 0.65rem;
  margin: 0 auto 2rem;
  font-family: var(--font-flow);
  font-size: clamp(1.15rem, 2.8vw, 1.45rem);
  font-weight: 500;
  letter-spacing: 0.04em;
  color: var(--accent);
}

.flow-node,
.flow-sep {
  opacity: 0;
  transform: translateY(14px);
}

.flow-chain.played .flow-node,
.flow-chain.played .flow-sep {
  animation: flow-in 0.65s var(--ease) forwards;
  animation-delay: calc(var(--i, 0) * 0.14s);
}

.flow-chain.played.floating {
  animation: flow-float 4.5s ease-in-out 0.9s infinite;
}

.flow-sep {
  color: color-mix(in srgb, var(--accent-soft) 70%, var(--muted));
  font-weight: 400;
  opacity: 0;
}

@keyframes flow-in {
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes flow-float {
  0%,
  100% {
    transform: translateY(0);
  }
  50% {
    transform: translateY(-7px);
  }
}

@keyframes hero-mark-float {
  0%,
  100% {
    transform: translateY(0);
  }
  50% {
    transform: translateY(-8px);
  }
}

.hero-cta {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 0.75rem;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 44px;
  padding: 0.55rem 1.25rem;
  border-radius: var(--radius);
  font-weight: 600;
  font-size: 0.95rem;
  text-decoration: none;
  border: 1px solid transparent;
  transition: transform 0.2s var(--ease), background 0.2s var(--ease), box-shadow 0.2s var(--ease), border-color 0.2s;
}

.btn:hover {
  transform: translateY(-2px);
}

.btn:active {
  transform: translateY(0);
}

.btn.primary {
  background: var(--accent);
  color: #fff;
  box-shadow: 0 6px 18px color-mix(in srgb, var(--accent) 32%, transparent);
}

.btn.primary:hover {
  background: var(--accent-soft);
}

.btn.ghost {
  background: transparent;
  color: var(--accent);
  border-color: color-mix(in srgb, var(--accent) 40%, transparent);
}

.btn.ghost:hover {
  background: var(--accent-wash);
  border-color: var(--accent);
}

.btn.disabled,
.btn[aria-disabled="true"] {
  opacity: 0.55;
  cursor: not-allowed;
  pointer-events: none;
  transform: none;
  box-shadow: none;
}

/* Docs */
.docs {
  border-top: 1px solid var(--line);
}

.docs-reveal {
  opacity: 0;
  transform: translateY(22px);
  transition: opacity 0.7s var(--ease), transform 0.7s var(--ease);
}

.docs-reveal.in {
  opacity: 1;
  transform: none;
}

.docs-layout {
  display: grid;
  grid-template-columns: 220px 1fr;
  gap: 2rem;
  align-items: start;
}

.docs-toc {
  position: sticky;
  top: calc(var(--header-h) + 1rem);
  display: flex;
  flex-direction: column;
  gap: 1.15rem;
}

.toc-group {
  display: flex;
  flex-direction: column;
  gap: 0.2rem;
}

.toc-major {
  display: block;
  padding: 0.35rem 0.55rem;
  color: var(--ink);
  text-decoration: none;
  font-size: 0.95rem;
  font-weight: 700;
  border-radius: var(--radius);
  border-left: 2px solid transparent;
}

.toc-major:hover,
.toc-major.active {
  color: var(--accent);
  background: color-mix(in srgb, var(--accent-wash) 55%, transparent);
  border-left-color: var(--accent);
}

.toc-minor {
  display: block;
  padding: 0.28rem 0.55rem 0.28rem 0.95rem;
  color: var(--muted);
  text-decoration: none;
  font-size: 0.88rem;
  font-weight: 500;
  border-radius: var(--radius);
  border-left: 2px solid transparent;
}

.toc-minor:hover,
.toc-minor.active {
  color: var(--accent);
  background: color-mix(in srgb, var(--accent-wash) 50%, transparent);
  border-left-color: var(--accent-soft);
}

.doc-block {
  margin-bottom: 2.75rem;
  scroll-margin-top: calc(var(--header-h) + 16px);
}

.doc-block:last-child {
  margin-bottom: 0;
}

.doc-block h3 {
  margin: 0 0 1rem;
  font-family: var(--font-display);
  font-size: 1.55rem;
  font-weight: 700;
  letter-spacing: -0.02em;
  scroll-margin-top: calc(var(--header-h) + 16px);
}

.doc-block h4 {
  margin: 1.5rem 0 0.65rem;
  font-size: 1.05rem;
  font-weight: 600;
  color: var(--ink);
  scroll-margin-top: calc(var(--header-h) + 16px);
}

.doc-block h4:first-of-type {
  margin-top: 1.15rem;
}

.doc-block p {
  margin: 0 0 0.95rem;
  color: var(--muted);
  font-size: 0.98rem;
  line-height: 1.75;
  max-width: 42rem;
}

.doc-block p:has(> strong:only-child) {
  margin-bottom: 0.35rem;
  color: var(--ink);
  scroll-margin-top: calc(var(--header-h) + 16px);
}

.doc-block p:last-child {
  margin-bottom: 0;
}

.doc-block strong {
  color: var(--ink);
  font-weight: 600;
}

/* Download */
.download {
  border-top: 1px solid var(--line);
  padding-bottom: 4rem;
}

.download-panel {
  display: flex;
  justify-content: center;
  flex-wrap: wrap;
  gap: 1.5rem;
}

.download-card {
  width: 220px;
  max-width: 100%;
  padding: 1.35rem 1.1rem;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: color-mix(in srgb, var(--surface) 80%, var(--bg));
  text-align: center;
  animation: card-float 4.8s ease-in-out var(--float-delay, 0s) infinite;
  transition: border-color 0.25s var(--ease), box-shadow 0.25s var(--ease);
}

.download-card:hover {
  border-color: color-mix(in srgb, var(--accent) 45%, transparent);
  box-shadow: 0 12px 28px color-mix(in srgb, var(--accent) 12%, transparent);
  animation-play-state: paused;
  transform: translateY(-5px);
}

.download-card h3 {
  margin: 0 0 0.4rem;
  font-size: 1.05rem;
}

.download-card p {
  margin: 0 0 1.1rem;
  color: var(--muted);
  font-size: 0.92rem;
}

.download-card .btn {
  margin-inline: auto;
}

@keyframes card-float {
  0%,
  100% {
    transform: translateY(0);
  }
  50% {
    transform: translateY(-6px);
  }
}

.download-note {
  margin: 1.5rem 0 0;
  color: var(--muted);
  font-size: 0.9rem;
  text-align: center;
}

.site-footer {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  flex-wrap: wrap;
  padding: 1.25rem clamp(1rem, 4vw, 2.5rem) 2rem;
  max-width: 1100px;
  margin-inline: auto;
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-size: 0.85rem;
}

/* Reveal */
.reveal {
  opacity: 0;
  transform: translateY(16px);
  transition: opacity 0.7s var(--ease), transform 0.7s var(--ease);
}

.reveal.in {
  opacity: 1;
  transform: none;
}

.delay-1 {
  transition-delay: 0.08s;
}
.delay-2 {
  transition-delay: 0.16s;
}
.delay-3 {
  transition-delay: 0.24s;
}

/* Responsive */
@media (max-width: 860px) {
  .docs-layout {
    grid-template-columns: 1fr;
  }

  .docs-toc {
    position: static;
  }

  .toc-group {
    width: 100%;
  }
}

@media (max-width: 640px) {
  .nav-toggle {
    display: flex;
  }

  .nav {
    position: absolute;
    top: var(--header-h);
    left: 0;
    right: 0;
    display: none;
    flex-direction: column;
    padding: 0.75rem 1rem 1rem;
    background: color-mix(in srgb, var(--bg) 96%, transparent);
    backdrop-filter: blur(12px);
    border-bottom: 1px solid var(--line);
  }

  .nav.open {
    display: flex;
  }

  .nav a {
    width: 100%;
  }

  .hero {
    min-height: auto;
  }

  .site-footer {
    flex-direction: column;
    align-items: flex-start;
  }
}

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

  .reveal,
  .docs-reveal,
  .btn,
  .download-card,
  .hero-mark.reveal.in,
  .flow-chain.played.floating {
    animation: none !important;
    transition: none !important;
    opacity: 1 !important;
    transform: none !important;
  }

  .flow-chain .flow-node,
  .flow-chain .flow-sep {
    opacity: 1 !important;
    transform: none !important;
    animation: none !important;
  }
}