:root {
  --bg: #0a0a14;
  --bg-soft: #11111e;
  --bg-card: #161628;
  --fg: #e9ecf1;
  --fg-muted: #a8acbf;
  --accent: #ffb74d;
  --accent-2: #82b1ff;
  --accent-3: #b39ddb;
  --line: #2a2a40;
  --warning: #ff8a65;
  --max: 1100px;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--fg);
  font-family: 'Inter', 'Segoe UI', system-ui, -apple-system, sans-serif;
  line-height: 1.65;
  font-size: 16px;
  text-rendering: optimizeLegibility;
}

body {
  background:
    radial-gradient(1200px 600px at 20% -10%, rgba(130, 177, 255, 0.10), transparent 60%),
    radial-gradient(900px 600px at 90% 10%, rgba(255, 183, 77, 0.07), transparent 60%),
    var(--bg);
  min-height: 100vh;
}

a {
  color: var(--accent-2);
  text-decoration: none;
  border-bottom: 1px dotted rgba(130, 177, 255, 0.4);
}
a:hover { color: var(--accent); border-bottom-color: var(--accent); }

header.site-header {
  border-bottom: 1px solid var(--line);
  padding: 1.6rem 2rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 1rem;
  background: rgba(10, 10, 20, 0.7);
  backdrop-filter: blur(8px);
  position: sticky;
  top: 0;
  z-index: 10;
}

header.site-header .brand {
  font-weight: 600;
  letter-spacing: 0.02em;
  font-size: 1.05rem;
}
header.site-header .brand small {
  display: block;
  font-weight: 400;
  color: var(--fg-muted);
  font-size: 0.78rem;
  letter-spacing: 0.05em;
  text-transform: uppercase;
  margin-top: 2px;
}

nav.lang-switch a {
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: 0.35rem 0.9rem;
  font-size: 0.85rem;
  margin-left: 0.5rem;
  color: var(--fg-muted);
}
nav.lang-switch a.active {
  border-color: var(--accent);
  color: var(--accent);
  background: rgba(255, 183, 77, 0.08);
}

main {
  max-width: var(--max);
  margin: 0 auto;
  padding: 2.5rem 1.5rem 6rem;
}

.hero {
  text-align: center;
  padding: 2.5rem 1rem 3rem;
  border-bottom: 1px solid var(--line);
  margin-bottom: 3rem;
}
.hero h1 {
  font-size: clamp(1.8rem, 4vw, 2.8rem);
  font-weight: 700;
  letter-spacing: -0.01em;
  line-height: 1.15;
  margin: 0 0 0.6rem;
  background: linear-gradient(120deg, #ffd180, #82b1ff 60%, #b39ddb);
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}
.hero p.lead {
  color: var(--fg-muted);
  font-size: 1.1rem;
  max-width: 720px;
  margin: 0 auto 1.5rem;
}
.hero .meta {
  font-size: 0.85rem;
  color: var(--fg-muted);
  letter-spacing: 0.04em;
}
.hero .meta span { display: inline-block; padding: 0 0.6rem; }
.hero .meta span + span { border-left: 1px solid var(--line); }

.toc {
  background: var(--bg-card);
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 1.4rem 1.6rem;
  margin-bottom: 3rem;
}
.toc h2 {
  margin: 0 0 0.8rem;
  font-size: 0.78rem;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--accent);
  font-weight: 600;
}
.toc ol { margin: 0; padding-left: 1.4rem; }
.toc li { margin: 0.2rem 0; color: var(--fg-muted); }
.toc li a { color: var(--fg); border: none; }
.toc li a:hover { color: var(--accent); }

section.chapter {
  margin: 0 0 5rem;
  scroll-margin-top: 100px;
}

section.chapter > .label {
  display: inline-block;
  font-size: 0.72rem;
  letter-spacing: 0.2em;
  text-transform: uppercase;
  color: var(--accent);
  border: 1px solid rgba(255, 183, 77, 0.4);
  border-radius: 999px;
  padding: 0.2rem 0.8rem;
  margin-bottom: 1rem;
}
section.chapter > h2 {
  font-size: clamp(1.5rem, 2.6vw, 2rem);
  margin: 0 0 1rem;
  font-weight: 600;
  line-height: 1.25;
}
section.chapter > .intro {
  color: var(--fg-muted);
  margin: 0 0 2rem;
  max-width: 750px;
}

.figure {
  margin: 2rem 0;
  border: 1px solid var(--line);
  border-radius: 10px;
  background: var(--bg-soft);
  overflow: hidden;
}
.figure img {
  width: 100%;
  height: auto;
  display: block;
  background: #000;
}
.figure figcaption {
  padding: 1rem 1.3rem;
  font-size: 0.92rem;
  color: var(--fg-muted);
  border-top: 1px solid var(--line);
}
.figure figcaption .tag {
  display: inline-block;
  font-family: 'JetBrains Mono', 'Consolas', monospace;
  font-size: 0.72rem;
  color: var(--accent);
  letter-spacing: 0.1em;
  text-transform: uppercase;
  margin-right: 0.6rem;
  border: 1px solid rgba(255, 183, 77, 0.3);
  padding: 0.1rem 0.4rem;
  border-radius: 4px;
}
.figure figcaption strong {
  display: block;
  color: var(--fg);
  font-weight: 600;
  margin-bottom: 0.3rem;
}

.callout {
  border-left: 3px solid var(--accent-2);
  background: rgba(130, 177, 255, 0.06);
  padding: 0.9rem 1.2rem;
  margin: 1.5rem 0;
  border-radius: 0 8px 8px 0;
  font-size: 0.95rem;
}
.callout.warning {
  border-left-color: var(--warning);
  background: rgba(255, 138, 101, 0.08);
}
.callout.note {
  border-left-color: var(--accent-3);
  background: rgba(179, 157, 219, 0.08);
}
.callout strong {
  display: block;
  color: var(--accent-2);
  font-size: 0.78rem;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  margin-bottom: 0.3rem;
}
.callout.warning strong { color: var(--warning); }
.callout.note strong { color: var(--accent-3); }

.grid-five {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 1rem;
  margin: 1.5rem 0;
}
.grid-five .card {
  background: var(--bg-card);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 1rem;
  font-size: 0.88rem;
}
.grid-five .card h4 {
  margin: 0 0 0.4rem;
  color: var(--accent);
  font-size: 0.95rem;
}

table {
  width: 100%;
  border-collapse: collapse;
  margin: 1.5rem 0;
  font-size: 0.92rem;
}
table th, table td {
  padding: 0.65rem 0.8rem;
  border-bottom: 1px solid var(--line);
  text-align: left;
}
table th {
  color: var(--accent);
  font-weight: 600;
  font-size: 0.78rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

footer {
  border-top: 1px solid var(--line);
  padding: 2rem 1.5rem;
  text-align: center;
  color: var(--fg-muted);
  font-size: 0.85rem;
}
footer p { margin: 0.4rem 0; }

code, .mono {
  font-family: 'JetBrains Mono', 'Consolas', monospace;
  background: rgba(255, 183, 77, 0.08);
  color: var(--accent);
  padding: 0.05rem 0.35rem;
  border-radius: 4px;
  font-size: 0.92em;
}

.lang-home {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  min-height: 100vh;
  padding: 2rem;
  text-align: center;
}
.lang-home h1 {
  font-size: clamp(2rem, 5vw, 3.5rem);
  margin: 0 0 0.4rem;
  background: linear-gradient(120deg, #ffd180, #82b1ff 60%, #b39ddb);
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}
.lang-home p.author {
  color: var(--fg-muted);
  margin: 0 0 3rem;
  letter-spacing: 0.05em;
}
.lang-home .choices {
  display: flex;
  gap: 1.5rem;
  flex-wrap: wrap;
  justify-content: center;
}
.lang-home .choices a {
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 1.5rem 2.5rem;
  min-width: 220px;
  text-align: center;
  background: var(--bg-card);
  transition: all 0.2s ease;
}
.lang-home .choices a:hover {
  border-color: var(--accent);
  background: rgba(255, 183, 77, 0.06);
  transform: translateY(-2px);
}
.lang-home .choices a strong {
  display: block;
  font-size: 1.4rem;
  color: var(--fg);
  margin-bottom: 0.3rem;
}
.lang-home .choices a span {
  color: var(--fg-muted);
  font-size: 0.9rem;
}
.lang-home .choices a.disabled {
  opacity: 0.55;
  cursor: not-allowed;
}
.lang-home .footer-note {
  margin-top: 4rem;
  font-size: 0.85rem;
  color: var(--fg-muted);
  max-width: 500px;
}

@media (max-width: 720px) {
  header.site-header { padding: 1rem; }
  main { padding: 1.5rem 1rem 4rem; }
  .figure figcaption { padding: 0.8rem 1rem; font-size: 0.88rem; }
}