:root {
  --color-deep: #0B1E3A;
  --color-ink: #E6E8EB;
  --color-muted: #B3C0CC;
  --color-slate: #C0C8D0;
  --color-moss: #5E7A5C;
  --color-clay: #B85C38;
  --color-cream: #F5F0E6;
  --color-violet: #8A6DE9;
  --color-orange: #FF8C42;
  --color-cyan: #4EE1E1;
  --font-sans: "PingFang SC", "Noto Sans SC", "Microsoft YaHei", sans-serif;
  --font-mono: "Roboto Mono", "Courier New", monospace;
  --gradient-signal: linear-gradient(135deg, var(--color-violet) 0%, var(--color-orange) 55%, var(--color-cyan) 100%);
  --header-height: 76px;
  --shell-pad: clamp(20px, 4vw, 40px);
  --border-print: 1px dashed rgba(192, 200, 208, 0.25);
}

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

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

body {
  margin: 0;
  min-height: 100vh;
  background:
    radial-gradient(circle at 12% 8%, rgba(138, 109, 233, 0.18), transparent 30%),
    radial-gradient(circle at 88% 20%, rgba(78, 225, 225, 0.10), transparent 34%),
    radial-gradient(circle at 70% 85%, rgba(255, 140, 66, 0.08), transparent 28%),
    var(--color-deep);
  color: var(--color-ink);
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.75;
}

h1, h2, h3, h4, p, ul, ol, dl, figure, blockquote {
  margin-top: 0;
}

a {
  color: var(--color-cyan);
  text-decoration: none;
  border-bottom: 1px solid transparent;
  transition: color 0.2s ease, border-color 0.2s ease;
}

a:hover {
  color: var(--color-orange);
  border-bottom-color: currentColor;
}

button {
  font-family: inherit;
}

:focus-visible {
  outline: 2px solid var(--color-cyan);
  outline-offset: 4px;
}

[hidden] {
  display: none !important;
}

.visually-hidden {
  position: absolute !important;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
  white-space: nowrap;
  border: 0;
}

.skip-link {
  position: fixed;
  left: 16px;
  top: -120px;
  z-index: 999;
  padding: 12px 18px;
  background: var(--color-orange);
  color: var(--color-deep);
  font-weight: 900;
  font-size: 14px;
  border: 0;
}

.skip-link:focus {
  top: 16px;
  color: var(--color-deep);
  border: 0;
}

#main-content {
  display: block;
  scroll-margin-top: calc(var(--header-height) + 16px);
}

.main-content {
  min-height: 60vh;
}

.site-shell {
  width: 100%;
  max-width: 1320px;
  margin-inline: auto;
  padding-inline: var(--shell-pad);
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(11, 30, 58, 0.86);
  -webkit-backdrop-filter: blur(10px);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid rgba(78, 225, 225, 0.18);
}

.site-header::after {
  content: "";
  display: block;
  height: 2px;
  background: linear-gradient(90deg, var(--color-violet), var(--color-orange), var(--color-cyan));
  transform: scaleX(0.32);
  transform-origin: left;
}

.site-header__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
  min-height: var(--header-height);
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 12px;
  border: 0;
}

.brand:hover {
  border: 0;
}

.brand__mark {
  display: grid;
  place-items: center;
  width: 44px;
  height: 44px;
  background: var(--gradient-signal);
  color: var(--color-deep);
  font-size: 22px;
  font-weight: 900;
  border-radius: 14px 4px 14px 4px;
  box-shadow: 0 0 24px rgba(138, 109, 233, 0.35);
}

.brand__text {
  display: block;
  color: var(--color-ink);
  font-weight: 900;
  font-size: 18px;
  line-height: 1.2;
  letter-spacing: 0.02em;
}

.brand__text small {
  display: block;
  font-family: var(--font-mono);
  font-size: 10px;
  letter-spacing: 0.14em;
  color: var(--color-cyan);
}

.site-nav__list {
  display: flex;
  align-items: center;
  gap: 6px;
  margin: 0;
  padding: 0;
  list-style: none;
}

.site-nav__link {
  position: relative;
  display: flex;
  align-items: baseline;
  gap: 6px;
  padding: 10px 10px 8px;
  color: var(--color-muted);
  font-size: 14px;
  font-weight: 500;
  border: 0;
  border-bottom: 2px solid transparent;
}

.site-nav__link:hover {
  color: var(--color-ink);
  border-bottom-color: var(--color-cyan);
}

.site-nav__index {
  font-family: var(--font-mono);
  font-size: 10px;
  color: var(--color-cyan);
  opacity: 0.85;
}

.site-nav__link[aria-current="page"] {
  color: var(--color-ink);
}

.site-nav__link[aria-current="page"]::after {
  content: "";
  position: absolute;
  left: 10px;
  right: 10px;
  bottom: -2px;
  height: 2px;
  background: linear-gradient(90deg, var(--color-orange), var(--color-violet));
}

.nav-toggle {
  display: none;
  align-items: center;
  justify-content: center;
  width: 44px;
  height: 44px;
  padding: 0;
  background: transparent;
  color: var(--color-ink);
  border: 1px solid rgba(78, 225, 225, 0.4);
  border-radius: 8px;
  cursor: pointer;
}

.nav-toggle__bars {
  position: relative;
  display: block;
  width: 20px;
  height: 2px;
  background: currentColor;
}

.nav-toggle__bars::before,
.nav-toggle__bars::after {
  content: "";
  position: absolute;
  left: 0;
  width: 20px;
  height: 2px;
  background: currentColor;
}

.nav-toggle__bars::before {
  top: -6px;
}

.nav-toggle__bars::after {
  top: 6px;
}

.nav-toggle[aria-expanded="true"] .nav-toggle__bars {
  background: transparent;
}

.nav-toggle[aria-expanded="true"] .nav-toggle__bars::before {
  transform: translateY(6px) rotate(45deg);
}

.nav-toggle[aria-expanded="true"] .nav-toggle__bars::after {
  transform: translateY(-6px) rotate(-45deg);
}

.site-footer {
  position: relative;
  margin-top: 80px;
  background: linear-gradient(180deg, #071426 0%, var(--color-deep) 100%);
  border-top: 1px solid rgba(78, 225, 225, 0.15);
}

.site-footer::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: linear-gradient(90deg, var(--color-violet), var(--color-orange), var(--color-cyan));
  opacity: 0.85;
}

.site-footer__inner {
  display: grid;
  grid-template-columns: 1fr 1.4fr;
  gap: 40px;
  padding-top: 48px;
  padding-bottom: 28px;
}

.site-footer__brand {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  gap: 14px;
}

.brand__mark--footer {
  width: 48px;
  height: 48px;
  font-size: 24px;
}

.site-footer__trust {
  max-width: 36ch;
  margin: 0;
  color: var(--color-muted);
  font-size: 13px;
  line-height: 1.8;
}

.site-footer__cols {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 28px;
}

.site-footer__heading {
  margin: 0 0 12px;
  color: var(--color-cyan);
  font-family: var(--font-mono);
  font-size: 13px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.site-footer__col p,
.site-footer__col ul {
  margin: 0;
  color: var(--color-muted);
  font-size: 13px;
  line-height: 1.8;
}

.site-footer__col ul {
  padding: 0;
  list-style: none;
}

.site-footer__col a {
  color: var(--color-muted);
}

.site-footer__col a:hover {
  color: var(--color-cyan);
}

.site-footer__meta {
  grid-column: 1 / -1;
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: 8px;
  margin-top: 8px;
  padding-top: 16px;
  border-top: 1px dashed rgba(192, 200, 208, 0.3);
  font-family: var(--font-mono);
  font-size: 13px;
  color: var(--color-muted);
}

.section {
  padding: clamp(56px, 10vw, 100px) 0;
}

.section--tight {
  padding: 40px 0;
}

.section--stripe {
  border-top: var(--border-print);
  border-bottom: var(--border-print);
  background: rgba(255, 255, 255, 0.015);
}

.page-header {
  position: relative;
  padding: clamp(48px, 8vw, 88px) 0 32px;
}

.page-header::before {
  content: "";
  position: absolute;
  top: 0;
  left: 0;
  width: 18%;
  height: 4px;
  background: var(--gradient-signal);
}

.page-title {
  margin: 0;
  font-size: clamp(38px, 7vw, 72px);
  font-weight: 900;
  line-height: 1.05;
  letter-spacing: -0.04em;
}

.page-subtitle {
  margin: 14px 0 0;
  max-width: 58ch;
  color: var(--color-muted);
  font-size: clamp(15px, 2vw, 18px);
}

.breadcrumbs {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin: 0 0 28px;
  padding: 0;
  list-style: none;
  font-size: 13px;
}

.breadcrumbs li::before {
  content: "/";
  margin-right: 8px;
  color: var(--color-muted);
}

.breadcrumbs li:first-child::before {
  content: "";
  margin: 0;
}

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

.breadcrumbs [aria-current="page"] {
  color: var(--color-ink);
}

.chapter {
  position: relative;
  padding: 48px 0;
  border-bottom: var(--border-print);
}

.chapter__header {
  display: grid;
  grid-template-columns: 120px 1fr;
  gap: 24px;
  align-items: start;
}

.chapter__number {
  font-family: var(--font-mono);
  font-size: clamp(48px, 7vw, 72px);
  line-height: 1;
  color: transparent;
  background: var(--gradient-signal);
  -webkit-background-clip: text;
  background-clip: text;
}

.chapter__title {
  margin: 0;
  font-size: clamp(24px, 3.2vw, 36px);
  font-weight: 900;
  line-height: 1.2;
}

.chapter__lead {
  margin: 8px 0 0;
  max-width: 72ch;
  color: var(--color-muted);
}

.grid {
  display: grid;
  gap: 24px;
}

.grid--2 {
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.grid--3 {
  grid-template-columns: repeat(3, minmax(0, 1fr));
}

.card {
  position: relative;
  padding: 24px;
  background: linear-gradient(145deg, rgba(78, 225, 225, 0.06), rgba(138, 109, 233, 0.04));
  border: 1px solid rgba(192, 200, 208, 0.18);
  transition: transform 0.2s ease, border-color 0.2s ease;
}

.card::before {
  content: attr(data-index);
  position: absolute;
  top: 18px;
  right: 18px;
  font-family: var(--font-mono);
  font-size: 12px;
  color: rgba(78, 225, 225, 0.45);
}

.card:hover {
  transform: translateY(-4px);
  border-color: rgba(78, 225, 225, 0.5);
}

.card--accent::after {
  content: "";
  position: absolute;
  left: 0;
  top: 0;
  width: 4px;
  height: 100%;
  background: var(--gradient-signal);
}

.card__title {
  margin: 0 0 8px;
  font-size: 18px;
  font-weight: 900;
}

.card__text {
  margin: 0;
  color: var(--color-muted);
  font-size: 14px;
  line-height: 1.7;
}

.tag,
.label {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 4px 12px;
  font-size: 12px;
  line-height: 1.5;
  border: 1px solid rgba(78, 225, 225, 0.35);
  color: var(--color-cyan);
  background: rgba(11, 30, 58, 0.6);
  font-family: var(--font-mono);
}

.tag {
  color: var(--color-ink);
  background: rgba(138, 109, 233, 0.15);
  border-color: rgba(138, 109, 233, 0.35);
}

.label {
  text-transform: uppercase;
  letter-spacing: 0.12em;
}

.button {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  padding: 10px 18px;
  font-size: 14px;
  font-weight: 700;
  line-height: 1.4;
  border: 1px solid transparent;
  cursor: pointer;
  text-decoration: none;
}

.button--primary {
  background: var(--color-clay);
  border-color: var(--color-clay);
  color: #fff;
}

.button--primary:hover {
  background: #c96e48;
  border-color: #c96e48;
  color: #fff;
}

.button--ghost {
  background: transparent;
  border-color: rgba(78, 225, 225, 0.55);
  color: var(--color-cyan);
}

.button--ghost:hover {
  background: rgba(78, 225, 225, 0.08);
  color: var(--color-cyan);
}

.filter-bar {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

.filter-button {
  padding: 8px 16px;
  background: transparent;
  border: 1px solid rgba(78, 225, 225, 0.35);
  color: var(--color-muted);
  font-size: 14px;
  line-height: 1.4;
  cursor: pointer;
  transition: background 0.2s ease, color 0.2s ease, border-color 0.2s ease;
}

.filter-button:hover {
  color: var(--color-ink);
  border-color: var(--color-cyan);
}

.filter-button[aria-pressed="true"] {
  background: var(--color-violet);
  border-color: var(--color-violet);
  color: #fff;
}

.panel {
  padding: 24px;
  background: rgba(11, 30, 58, 0.8);
  border: 1px solid rgba(78, 225, 225, 0.2);
}

.panel__heading {
  margin: 0 0 8px;
  color: var(--color-cyan);
  font-family: var(--font-mono);
  font-size: 14px;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.term-list {
  margin: 0;
  padding: 0;
}

.term-list__item {
  display: grid;
  grid-template-columns: 180px 1fr;
  gap: 16px;
  padding: 10px 0;
  border-bottom: var(--border-print);
}

.term-list dt {
  font-family: var(--font-mono);
  font-size: 13px;
  color: var(--color-cyan);
}

.term-list dd {
  margin: 0;
  color: var(--color-muted);
  font-size: 14px;
}

.image-frame {
  position: relative;
  display: block;
  width: 100%;
  aspect-ratio: 16 / 9;
  overflow: hidden;
  border: 1px solid rgba(78, 225, 225, 0.28);
  background: linear-gradient(145deg, rgba(138, 109, 233, 0.18), rgba(11, 30, 58, 0.9));
}

.image-frame::before {
  content: "";
  position: absolute;
  inset: 0;
  background:
    linear-gradient(rgba(78, 225, 225, 0.12) 1px, transparent 1px),
    linear-gradient(90deg, rgba(78, 225, 225, 0.12) 1px, transparent 1px);
  background-size: 32px 32px;
  mix-blend-mode: screen;
  pointer-events: none;
}

.image-frame::after {
  content: attr(data-caption);
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  padding: 28px 12px 10px;
  font-family: var(--font-mono);
  font-size: 12px;
  color: var(--color-cyan);
  background: linear-gradient(transparent, rgba(11, 30, 58, 0.85));
  pointer-events: none;
}

@media (max-width: 980px) {
  .site-header__inner {
    gap: 16px;
  }

  .site-nav {
    position: absolute;
    top: calc(100% - 2px);
    left: 0;
    right: 0;
    display: none;
    background: rgba(7, 20, 38, 0.98);
    border-bottom: 1px solid var(--color-cyan);
    box-shadow: 0 18px 30px rgba(0, 0, 0, 0.3);
  }

  .site-nav[data-open] {
    display: block;
  }

  .site-nav__list {
    flex-direction: column;
    align-items: stretch;
    gap: 0;
    padding: 8px 16px 16px;
  }

  .site-nav__link {
    justify-content: space-between;
    padding: 14px 8px;
    border-bottom: 1px solid rgba(78, 225, 225, 0.1);
  }

  .site-nav__link[aria-current="page"] {
    background: linear-gradient(90deg, rgba(138, 109, 233, 0.25), transparent);
  }

  .site-nav__link[aria-current="page"]::after {
    display: none;
  }

  .nav-toggle {
    display: inline-flex;
  }

  .site-footer__inner {
    grid-template-columns: 1fr;
    gap: 32px;
  }

  .site-footer__meta {
    grid-column: 1;
  }
}

@media (max-width: 720px) {
  .chapter__header {
    grid-template-columns: 1fr;
  }

  .chapter__number {
    line-height: 0.9;
  }

  .grid--2,
  .grid--3 {
    grid-template-columns: 1fr;
  }

  .site-footer__cols {
    grid-template-columns: 1fr;
  }

  .term-list__item {
    grid-template-columns: 1fr;
    gap: 4px;
  }
}

@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;
  }

  .card:hover {
    transform: none;
  }

  .nav-toggle__bars::before,
  .nav-toggle__bars::after {
    transition: none;
  }
}