/* ===== Reset & Tokens ===== */
*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  --c-bg: #0B0B0C;
  --c-surface: #171412;
  --c-paper: #F2EFE9;
  --c-paper-dim: #C9C5BC;
  --c-accent: #FF4D00;
  --c-accent-2: #00A3FF;
  --c-line: #8A9BAB;
  --c-alert: #6B2117;
  --c-layer: #2A241F;
  --font-display: "Noto Serif SC", "Songti SC", "STSong", "SimSun", Georgia, serif;
  --font-heading: "Noto Sans SC", "PingFang SC", "Microsoft YaHei", system-ui, -apple-system, sans-serif;
  --font-body: "Noto Sans SC", "PingFang SC", "Microsoft YaHei", system-ui, -apple-system, sans-serif;
  --font-mono: "Roboto Mono", "SFMono-Regular", "Cascadia Mono", Consolas, "Courier New", monospace;
  --header-h: 84px;
  --container-w: 1280px;
  --radius-pill: 999px;
  --transition-fast: 0.18s ease;
}

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

body {
  font-family: var(--font-body);
  font-size: 16px;
  line-height: 1.7;
  color: var(--c-paper);
  background-color: var(--c-bg);
  background-image:
    radial-gradient(circle at 85% 5%, rgba(0, 163, 255, 0.07), transparent 28%),
    radial-gradient(circle at 8% 22%, rgba(255, 77, 0, 0.05), transparent 24%),
    linear-gradient(rgba(242, 239, 233, 0.014) 1px, transparent 1px),
    linear-gradient(90deg, rgba(242, 239, 233, 0.014) 1px, transparent 1px);
  background-size: auto, auto, 56px 56px, 56px 56px;
  min-height: 100vh;
  padding-top: var(--header-h);
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

main {
  display: block;
}

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

img,
video {
  max-width: 100%;
  display: block;
}

button,
input,
select,
textarea {
  font-family: inherit;
  font-size: inherit;
  color: inherit;
}

button {
  background: none;
  border: none;
}

h1,
h2,
h3,
h4,
h5,
h6 {
  font-family: var(--font-heading);
  font-weight: 700;
  line-height: 1.25;
  margin: 0 0 12px;
}

h1 {
  font-size: 44px;
}

h2 {
  font-size: 32px;
}

h3 {
  font-size: 24px;
}

h4 {
  font-size: 18px;
}

p {
  margin-bottom: 16px;
}

a {
  color: var(--c-accent-2);
  text-decoration: none;
  transition: color var(--transition-fast);
}

a:hover {
  color: var(--c-accent);
}

ul,
ol {
  padding-left: 1.25em;
}

:focus-visible {
  outline: 2px solid var(--c-accent);
  outline-offset: 3px;
  border-radius: 2px;
}

::selection {
  background: var(--c-accent);
  color: var(--c-bg);
}

::-webkit-scrollbar {
  width: 10px;
}

::-webkit-scrollbar-track {
  background: var(--c-bg);
}

::-webkit-scrollbar-thumb {
  background: var(--c-layer);
  border-radius: 5px;
}

::-webkit-scrollbar-thumb:hover {
  background: var(--c-accent);
}

/* ===== Layout Utilities ===== */
.container {
  width: 100%;
  max-width: var(--container-w);
  margin-inline: auto;
  padding-inline: 20px;
}

.grid {
  display: grid;
  grid-template-columns: repeat(12, 1fr);
  gap: 24px;
}

.grid .span-3 {
  grid-column: span 3;
}

.grid .span-4 {
  grid-column: span 4;
}

.grid .span-5 {
  grid-column: span 5;
}

.grid .span-6 {
  grid-column: span 6;
}

.grid .span-7 {
  grid-column: span 7;
}

.grid .span-8 {
  grid-column: span 8;
}

.grid .span-12 {
  grid-column: span 12;
}

/* ===== Skip Link & Scroll Progress ===== */
.skip-link {
  position: fixed;
  top: -80px;
  left: 16px;
  z-index: 300;
  padding: 10px 20px;
  background: var(--c-accent);
  color: var(--c-bg);
  font-size: 14px;
  font-weight: 700;
  border-radius: 0 0 12px 12px;
  text-decoration: none;
  transition: top var(--transition-fast);
}

.skip-link:focus {
  top: 0;
}

.scroll-progress {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  z-index: 200;
  background: linear-gradient(90deg, var(--c-accent), var(--c-accent-2));
  transform: scaleX(0);
  transform-origin: left center;
  pointer-events: none;
}

/* ===== Header ===== */
.site-header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 120;
  padding: 12px 20px 0;
}

.header-inner {
  position: relative;
  max-width: var(--container-w);
  margin-inline: auto;
  display: flex;
  align-items: center;
  gap: 16px;
  background: rgba(23, 20, 18, 0.88);
  border: 1px solid rgba(138, 155, 171, 0.2);
  border-radius: var(--radius-pill);
  padding: 8px 10px 8px 8px;
  -webkit-backdrop-filter: blur(14px);
  backdrop-filter: blur(14px);
  box-shadow: 0 10px 30px rgba(0, 0, 0, 0.35);
}

/* ===== Brand ===== */
.site-brand {
  display: inline-flex;
  align-items: center;
  gap: 12px;
  flex-shrink: 0;
}

.brand-mark {
  position: relative;
  display: inline-grid;
  place-items: center;
  width: 42px;
  height: 42px;
  background: var(--c-bg);
  border: 1px solid var(--c-accent);
  border-radius: 12px 12px 12px 3px;
  font-family: var(--font-mono);
  font-weight: 700;
  font-size: 14px;
  letter-spacing: 0.02em;
  color: var(--c-accent);
  transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
}

.brand-mark-dot {
  position: absolute;
  top: 5px;
  right: 5px;
  width: 5px;
  height: 5px;
  border-radius: 50%;
  background: var(--c-accent-2);
  box-shadow: 0 0 8px rgba(0, 163, 255, 0.8);
}

.brand-text {
  display: flex;
  flex-direction: column;
  line-height: 1.15;
}

.brand-name {
  font-family: var(--font-heading);
  font-weight: 900;
  font-size: 18px;
  color: var(--c-paper);
  letter-spacing: 0.02em;
  transition: color var(--transition-fast);
}

.brand-tagline {
  font-family: var(--font-mono);
  font-size: 10px;
  font-weight: 500;
  letter-spacing: 0.3em;
  text-transform: uppercase;
  color: var(--c-accent);
}

.site-brand:hover .brand-mark {
  border-color: var(--c-accent-2);
  box-shadow: 0 0 0 3px rgba(0, 163, 255, 0.15);
}

.site-brand:hover .brand-name {
  color: var(--c-accent-2);
}

/* ===== Navigation ===== */
.site-nav {
  margin-left: auto;
}

.nav-list {
  display: flex;
  align-items: center;
  gap: 2px;
  list-style: none;
}

.nav-link {
  display: inline-flex;
  align-items: center;
  padding: 8px 14px;
  border-radius: var(--radius-pill);
  font-size: 14px;
  font-weight: 500;
  color: var(--c-paper-dim);
  white-space: nowrap;
  transition: color var(--transition-fast), background-color var(--transition-fast);
}

.nav-link:hover {
  color: var(--c-paper);
  background: rgba(242, 239, 233, 0.06);
}

.nav-link[aria-current="page"] {
  color: var(--c-bg);
  background: var(--c-accent);
  font-weight: 700;
}

.nav-toggle {
  display: none;
  flex-direction: column;
  justify-content: center;
  align-items: stretch;
  gap: 5px;
  width: 42px;
  height: 42px;
  padding: 10px;
  background: transparent;
  border: 1px solid var(--c-line);
  border-radius: 14px;
  cursor: pointer;
  transition: border-color var(--transition-fast);
}

.nav-toggle:hover {
  border-color: var(--c-accent);
}

.nav-toggle-bar {
  display: block;
  height: 2px;
  background: var(--c-paper);
  border-radius: 2px;
  transition: transform var(--transition-fast), opacity var(--transition-fast), background-color var(--transition-fast);
}

.nav-toggle:hover .nav-toggle-bar {
  background: var(--c-accent);
}

.nav-toggle.is-open .nav-toggle-bar:nth-child(1) {
  transform: translateY(7px) rotate(45deg);
}

.nav-toggle.is-open .nav-toggle-bar:nth-child(2) {
  opacity: 0;
}

.nav-toggle.is-open .nav-toggle-bar:nth-child(3) {
  transform: translateY(-7px) rotate(-45deg);
}

/* ===== Footer ===== */
.site-footer {
  position: relative;
  margin-top: 96px;
  padding: 64px 0 28px;
  background: linear-gradient(180deg, #12100E 0%, var(--c-surface) 140px);
  border-top: 1px solid rgba(138, 155, 171, 0.26);
}

.site-footer::before {
  content: "";
  position: absolute;
  top: -1px;
  left: 20px;
  width: 96px;
  height: 2px;
  background: var(--c-accent);
}

.footer-grid {
  display: grid;
  grid-template-columns: 1.7fr 1fr 1.3fr 0.9fr;
  gap: 40px;
}

.footer-col {
  min-width: 0;
}

.footer-brand {
  margin-bottom: 18px;
}

.footer-trust {
  max-width: 320px;
  margin: 0;
  padding-left: 14px;
  border-left: 2px solid var(--c-accent);
  font-size: 13px;
  line-height: 1.8;
  color: var(--c-paper-dim);
}

.footer-heading {
  margin: 0 0 16px;
  padding-bottom: 8px;
  border-bottom: 1px solid rgba(138, 155, 171, 0.22);
  font-family: var(--font-mono);
  font-size: 12px;
  font-weight: 500;
  letter-spacing: 0.2em;
  text-transform: uppercase;
  color: var(--c-paper-dim);
}

.footer-nav ul,
.footer-legal ul {
  list-style: none;
  padding: 0;
  display: grid;
  gap: 10px;
}

.footer-nav a,
.footer-legal a {
  color: var(--c-paper-dim);
  font-size: 14px;
}

.footer-nav a:hover,
.footer-legal a:hover {
  color: var(--c-accent-2);
}

.footer-meta p {
  margin: 0 0 8px;
  font-size: 13px;
  line-height: 1.7;
  color: var(--c-paper-dim);
}

.footer-bottom {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  margin-top: 48px;
  padding-top: 24px;
  border-top: 1px solid rgba(138, 155, 171, 0.18);
}

.copyright {
  margin: 0;
  font-family: var(--font-mono);
  font-size: 12px;
  color: var(--c-paper-dim);
}

.scroll-top {
  position: fixed;
  right: 24px;
  bottom: 24px;
  z-index: 90;
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 10px 18px;
  background: rgba(23, 20, 18, 0.9);
  -webkit-backdrop-filter: blur(8px);
  backdrop-filter: blur(8px);
  border: 1px solid var(--c-line);
  border-radius: var(--radius-pill);
  color: var(--c-paper-dim);
  font-size: 13px;
  font-weight: 500;
  cursor: pointer;
  opacity: 0;
  visibility: hidden;
  transform: translateY(8px);
  transition: opacity var(--transition-fast), transform var(--transition-fast), border-color var(--transition-fast), color var(--transition-fast), visibility var(--transition-fast);
}

.scroll-top.is-visible {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

.scroll-top:hover {
  border-color: var(--c-accent);
  color: var(--c-accent);
}

/* ===== Page Header & Breadcrumb ===== */
.page-header {
  padding: 40px 0 28px;
  margin-bottom: 40px;
  border-bottom: 1px solid rgba(138, 155, 171, 0.2);
}

.page-title {
  margin: 0 0 8px;
  font-family: var(--font-display);
  font-weight: 900;
  font-size: clamp(30px, 4vw, 44px);
  line-height: 1.16;
}

.page-subtitle {
  margin: 0;
  max-width: 680px;
  font-size: 16px;
  color: var(--c-paper-dim);
}

.breadcrumb {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 6px;
  margin: 0 0 32px;
  padding: 0;
  list-style: none;
  font-family: var(--font-mono);
  font-size: 12px;
  letter-spacing: 0.06em;
  color: var(--c-paper-dim);
}

.breadcrumb li {
  display: inline-flex;
  align-items: center;
  gap: 6px;
}

.breadcrumb li:not(:last-child)::after {
  content: "/";
  color: var(--c-line);
  opacity: 0.7;
}

.breadcrumb a {
  color: var(--c-paper-dim);
}

.breadcrumb a:hover {
  color: var(--c-accent-2);
}

.breadcrumb [aria-current="page"] {
  color: var(--c-paper);
}

/* ===== Section & Chapter ===== */
.section {
  padding-block: 48px;
}

.section + .section {
  border-top: 1px solid rgba(138, 155, 171, 0.2);
}

.section-label {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  margin: 0 0 12px;
  font-family: var(--font-mono);
  font-size: 12px;
  font-weight: 500;
  letter-spacing: 0.22em;
  text-transform: uppercase;
  color: var(--c-accent-2);
}

.section-label::before {
  content: "";
  width: 28px;
  height: 1px;
  background: var(--c-accent-2);
}

.chapter {
  display: grid;
  grid-template-columns: 96px 1fr;
  gap: 20px;
  align-items: start;
  margin-bottom: 40px;
}

.chapter-id {
  font-family: var(--font-display);
  font-weight: 900;
  font-size: clamp(56px, 6vw, 88px);
  line-height: 0.9;
  color: var(--c-accent);
}

.chapter-body h2,
.chapter-body h3 {
  margin-top: 4px;
}

.display-text {
  font-family: var(--font-display);
  font-weight: 900;
  line-height: 1.18;
  font-size: clamp(34px, 4vw, 50px);
}

.lead {
  font-size: 18px;
  line-height: 1.8;
  color: var(--c-paper-dim);
}

/* ===== Buttons ===== */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 10px 22px;
  border-radius: 4px;
  border: 1px solid transparent;
  font-size: 14px;
  font-weight: 700;
  letter-spacing: 0.04em;
  line-height: 1.4;
  text-decoration: none;
  cursor: pointer;
  transition: background-color var(--transition-fast), border-color var(--transition-fast), color var(--transition-fast);
}

.btn-primary {
  background: var(--c-accent);
  color: var(--c-bg);
}

.btn-primary:hover {
  background: #ff6a22;
  color: var(--c-bg);
}

.btn-ghost {
  background: transparent;
  border-color: var(--c-line);
  color: var(--c-paper);
}

.btn-ghost:hover {
  border-color: var(--c-accent-2);
  color: var(--c-accent-2);
}

/* ===== Panels & Frames ===== */
.ruled-panel {
  position: relative;
  background: var(--c-surface);
  border: 1px solid rgba(138, 155, 171, 0.22);
  padding: 28px 24px 24px;
  box-shadow: 6px 6px 0 rgba(0, 0, 0, 0.35);
}

.ruled-panel::before {
  content: "";
  position: absolute;
  top: 10px;
  left: 12px;
  right: 12px;
  height: 1px;
  background: repeating-linear-gradient(90deg, var(--c-line) 0 5px, transparent 5px 9px);
  opacity: 0.5;
}

.ruled-panel::after {
  content: "";
  position: absolute;
  right: 10px;
  bottom: 10px;
  width: 18px;
  height: 18px;
  border-right: 2px solid var(--c-accent);
  border-bottom: 2px solid var(--c-accent);
  opacity: 0.9;
}

.frame-window {
  position: relative;
  border: 1px solid var(--c-line);
  background: rgba(23, 20, 18, 0.5);
}

.frame-window::before,
.frame-window::after {
  content: "";
  position: absolute;
  width: 28px;
  height: 28px;
  z-index: 1;
  pointer-events: none;
}

.frame-window::before {
  top: -1px;
  left: -1px;
  border-top: 3px solid var(--c-accent);
  border-left: 3px solid var(--c-accent);
}

.frame-window::after {
  bottom: -1px;
  right: -1px;
  border-bottom: 3px solid var(--c-accent);
  border-right: 3px solid var(--c-accent);
}

/* ===== Metrics & Tags ===== */
.metric {
  display: flex;
  flex-direction: column;
  gap: 4px;
}

.metric-value {
  font-family: var(--font-mono);
  font-weight: 700;
  font-size: clamp(24px, 4vw, 32px);
  line-height: 1;
  color: var(--c-paper);
}

.metric-label {
  font-size: 13px;
  letter-spacing: 0.04em;
  color: var(--c-paper-dim);
}

.accent {
  color: var(--c-accent);
}

.accent--blue {
  color: var(--c-accent-2);
}

.data-tag {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 4px 10px;
  font-family: var(--font-mono);
  font-size: 12px;
  letter-spacing: 0.08em;
  border: 1px solid var(--c-line);
  border-radius: var(--radius-pill);
  color: var(--c-paper-dim);
  background: transparent;
}

.data-tag--accent {
  color: var(--c-accent);
  border-color: var(--c-accent);
}

.notice {
  background: rgba(107, 33, 23, 0.16);
  border: 1px solid var(--c-alert);
  padding: 14px 18px;
  font-size: 14px;
  color: var(--c-paper-dim);
}

.notice a {
  color: var(--c-accent);
}

/* ===== Image Frame ===== */
.image-frame {
  position: relative;
  display: block;
  overflow: hidden;
  aspect-ratio: 16 / 9;
  background:
    linear-gradient(rgba(255, 255, 255, 0.035) 1px, transparent 1px),
    linear-gradient(90deg, rgba(255, 255, 255, 0.035) 1px, transparent 1px),
    var(--c-surface);
  background-size: 24px 24px;
  border: 1px solid rgba(138, 155, 171, 0.3);
}

.image-frame img {
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.image-frame--tall {
  aspect-ratio: 3 / 4;
}

.image-frame--wide {
  aspect-ratio: 21 / 9;
}

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

/* ===== Responsive ===== */
@media (max-width: 920px) {
  .footer-grid {
    grid-template-columns: 1fr 1fr;
    gap: 32px;
  }

  .footer-col--brand {
    grid-column: 1 / -1;
  }
}

@media (max-width: 880px) {
  .nav-toggle {
    display: flex;
  }

  .site-nav {
    display: none;
    position: absolute;
    top: calc(100% + 10px);
    left: 0;
    right: 0;
    background: rgba(23, 20, 18, 0.96);
    border: 1px solid rgba(138, 155, 171, 0.25);
    border-radius: 18px;
    padding: 12px;
    box-shadow: 0 20px 40px rgba(0, 0, 0, 0.5);
  }

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

  .nav-list {
    flex-direction: column;
    align-items: stretch;
    gap: 2px;
  }

  .nav-link {
    display: block;
    padding: 12px 16px;
    border-radius: 12px;
  }

  .nav-link[aria-current="page"] {
    color: var(--c-accent);
    background: rgba(255, 77, 0, 0.1);
  }

  .grid {
    grid-template-columns: repeat(6, 1fr);
  }

  .grid .span-3,
  .grid .span-4,
  .grid .span-5,
  .grid .span-6 {
    grid-column: span 3;
  }

  .grid .span-7,
  .grid .span-8,
  .grid .span-12 {
    grid-column: span 6;
  }
}

@media (max-width: 560px) {
  .grid {
    grid-template-columns: 1fr;
  }

  .grid .span-3,
  .grid .span-4,
  .grid .span-5,
  .grid .span-6,
  .grid .span-7,
  .grid .span-8,
  .grid .span-12 {
    grid-column: 1 / -1;
  }

  .footer-grid {
    grid-template-columns: 1fr;
  }

  .footer-col--brand {
    grid-column: auto;
  }

  h1 {
    font-size: 32px;
  }

  h2 {
    font-size: 26px;
  }

  .chapter {
    grid-template-columns: 64px 1fr;
    gap: 14px;
  }
}

@media (max-width: 480px) {
  .site-header {
    padding: 8px 12px 0;
  }

  .brand-mark {
    width: 36px;
    height: 36px;
    font-size: 12px;
  }

  .brand-name {
    font-size: 16px;
  }

  .brand-tagline {
    display: none;
  }

  .scroll-top {
    right: 16px;
    bottom: 16px;
  }

  .site-footer {
    padding-top: 48px;
  }
}

/* ===== Reduced Motion ===== */
@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;
  }
}