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

html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
  scroll-padding-top: 96px;
}

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--font-body);
  font-size: 16px;
  font-weight: 400;
  line-height: 1.75;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  overflow-wrap: break-word;
}

h1, h2, h3, h4, h5, h6, p, figure, dl, dd, blockquote {
  margin: 0;
}

ul, ol {
  margin: 0;
  padding: 0;
  list-style: none;
}

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

a {
  color: inherit;
  text-decoration: none;
}

button {
  font: inherit;
  color: inherit;
  background: none;
  border: 0;
  padding: 0;
  cursor: pointer;
}

table {
  border-collapse: collapse;
  width: 100%;
}

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

/* ---------- tokens ---------- */
:root {
  --paper: #F7F8FA;
  --card: #FFFFFF;
  --ink: #111827;
  --muted: #5B6472;
  --line: #D9DEE7;
  --blue: #2F6BFF;
  --blue-deep: #1C4FD6;
  --orange: #FF7A3D;
  --orange-deep: #C4541F;
  --mint: #7BE0B8;
  --mint-deep: #17845C;
  --blue-tint: #EAF0FF;
  --orange-tint: #FFF0E8;

  --font-display: "Noto Serif SC", "Source Han Serif SC", "Songti SC", "STSong", serif;
  --font-body: "Noto Sans SC", "Source Han Sans SC", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  --font-mono: "IBM Plex Mono", "JetBrains Mono", "SFMono-Regular", Consolas, "Liberation Mono", monospace;

  --shell: 1280px;
  --gutter: clamp(20px, 4vw, 40px);
  --bar-h: 38px;
  --radius: 6px;
  --shadow: 0 20px 44px -38px rgba(17, 24, 39, 0.45);
  --scroll-progress: 0;
}

/* ---------- typography utilities ---------- */
.display {
  font-family: var(--font-display);
  font-weight: 600;
  font-size: clamp(32px, 5vw, 60px);
  line-height: 1.14;
  letter-spacing: -0.02em;
}

.lead {
  font-size: clamp(16px, 1.5vw, 18px);
  line-height: 1.8;
  color: var(--muted);
}

.prose {
  max-width: 72ch;
  font-size: 16.5px;
  line-height: 1.8;
}

.prose > * + * {
  margin-top: 1.05em;
}

.prose h3 {
  font-family: var(--font-display);
  font-weight: 600;
  font-size: clamp(19px, 2.2vw, 24px);
  line-height: 1.4;
  letter-spacing: -0.01em;
}

.mono {
  font-family: var(--font-mono);
  font-weight: 500;
  font-variant-numeric: tabular-nums;
  letter-spacing: 0.01em;
}

.eyebrow {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  font-family: var(--font-mono);
  font-size: 11px;
  font-weight: 500;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--blue);
}

.eyebrow::before {
  content: "";
  width: 22px;
  height: 1px;
  background: currentColor;
  flex: none;
}

.rule {
  height: 1px;
  border: 0;
  margin: 0;
  background: var(--line);
}

/* ---------- layout ---------- */
.container {
  width: 100%;
  max-width: var(--shell);
  margin: 0 auto;
  padding: 0 var(--gutter);
}

.container--narrow {
  max-width: 900px;
}

.section {
  padding: clamp(44px, 6.5vw, 88px) 0;
}

.section--tight {
  padding: clamp(28px, 4vw, 52px) 0;
}

.section--tinted {
  background: var(--card);
  border-top: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
}

.section-head {
  display: flex;
  flex-wrap: wrap;
  align-items: flex-end;
  justify-content: space-between;
  gap: 16px 28px;
  margin-bottom: clamp(22px, 3vw, 38px);
}

.section-title {
  font-family: var(--font-display);
  font-weight: 600;
  font-size: clamp(24px, 3.2vw, 36px);
  line-height: 1.28;
  letter-spacing: -0.015em;
}

.grid {
  display: grid;
  gap: clamp(16px, 2.4vw, 26px);
  grid-template-columns: minmax(0, 1fr);
}

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

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

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

@media (min-width: 720px) {
  .grid--halves { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .grid--thirds { grid-template-columns: repeat(2, minmax(0, 1fr)); }
}

@media (min-width: 900px) {
  .grid--split {
    grid-template-columns: minmax(0, 1.4fr) minmax(0, 1fr);
    gap: clamp(28px, 4.5vw, 64px);
  }
  .grid--thirds { grid-template-columns: repeat(3, minmax(0, 1fr)); }
}

/* ---------- buttons ---------- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 10px;
  padding: 12px 20px;
  border: 1px solid var(--line);
  border-radius: 4px;
  background: var(--card);
  color: var(--ink);
  font-size: 14px;
  font-weight: 700;
  letter-spacing: 0.01em;
  transition: background 0.15s ease, color 0.15s ease, border-color 0.15s ease, transform 0.15s ease;
}

.btn:hover {
  transform: translateY(-1px);
}

.btn--primary {
  background: var(--blue);
  border-color: var(--blue);
  color: #FFFFFF;
}

.btn--primary:hover {
  background: var(--blue-deep);
  border-color: var(--blue-deep);
}

.btn--accent {
  background: var(--orange);
  border-color: var(--orange);
  color: #FFFFFF;
}

.btn--accent:hover {
  background: var(--orange-deep);
  border-color: var(--orange-deep);
}

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

.btn--ghost:hover {
  border-color: var(--ink);
}

.btn__arrow {
  font-family: var(--font-mono);
  font-size: 12px;
  line-height: 1;
}

/* ---------- cards & tags ---------- */
.card {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: clamp(18px, 2.6vw, 26px);
  box-shadow: var(--shadow);
}

.card--frame {
  position: relative;
  padding: clamp(20px, 2.8vw, 30px);
}

.card--frame::before {
  content: "";
  position: absolute;
  inset: 6px;
  border: 1px solid var(--line);
  border-radius: 3px;
  opacity: 0.75;
  pointer-events: none;
}

.card--tint {
  background: var(--blue-tint);
  border-color: #CBD9FF;
}

.tag {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 3px 9px;
  border-radius: 3px;
  background: var(--blue-tint);
  color: var(--blue-deep);
  font-size: 11.5px;
  font-weight: 700;
  letter-spacing: 0.05em;
  white-space: nowrap;
}

.tag--accent {
  background: var(--orange-tint);
  color: var(--orange-deep);
}

.tag--mint {
  background: rgba(123, 224, 184, 0.22);
  color: var(--mint-deep);
}

.status-dot {
  display: inline-block;
  width: 7px;
  height: 7px;
  border-radius: 50%;
  background: var(--mint);
  flex: none;
}

.status-dot--blue { background: var(--blue); }
.status-dot--accent { background: var(--orange); }

/* ---------- breadcrumb ---------- */
.breadcrumb {
  padding: 14px 0 0;
}

.breadcrumb-list {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px;
  font-family: var(--font-mono);
  font-size: 11.5px;
  letter-spacing: 0.04em;
  color: var(--muted);
}

.breadcrumb-list li {
  display: flex;
  align-items: center;
  gap: 8px;
}

.breadcrumb-list li + li::before {
  content: "/";
  color: var(--line);
}

.breadcrumb-link {
  color: var(--muted);
  transition: color 0.15s ease;
}

.breadcrumb-link:hover {
  color: var(--blue);
}

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

/* ---------- figure ---------- */
.figure {
  display: flex;
  flex-direction: column;
  gap: 10px;
  margin: 0;
}

.figure-media {
  position: relative;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: linear-gradient(135deg, var(--blue-tint) 0%, var(--paper) 52%, var(--orange-tint) 100%);
  aspect-ratio: 16 / 10;
}

.figure-media > img,
.figure-media > picture > img {
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.figure-media--wide { aspect-ratio: 21 / 9; }
.figure-media--tall { aspect-ratio: 4 / 5; }

.figure-media--empty::before {
  content: "";
  position: absolute;
  inset: 0;
  background-image:
    linear-gradient(var(--line), var(--line)),
    linear-gradient(var(--line), var(--line));
  background-size: 1px 100%, 100% 1px;
  background-position: center center, center center;
  background-repeat: no-repeat;
  opacity: 0.8;
}

.figure-caption {
  font-family: var(--font-mono);
  font-size: 12px;
  letter-spacing: 0.02em;
  color: var(--muted);
}

/* ---------- skip link ---------- */
.skip-link {
  position: fixed;
  left: 16px;
  top: -100px;
  z-index: 200;
  padding: 10px 16px;
  border-radius: 0 0 4px 4px;
  background: var(--ink);
  color: #FFFFFF;
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 0.02em;
  transition: top 0.18s ease;
}

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

/* ---------- header ---------- */
.site-header {
  position: relative;
  z-index: 70;
  background: var(--card);
  border-bottom: 1px solid var(--line);
  padding-top: var(--bar-h);
}

.utility-bar {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 90;
  height: var(--bar-h);
  background: var(--ink);
  color: #FFFFFF;
}

.utility-bar::after {
  content: "";
  position: absolute;
  left: 0;
  bottom: 0;
  height: 2px;
  width: calc(var(--scroll-progress) * 100%);
  background: linear-gradient(90deg, var(--blue), var(--mint));
  transition: width 0.12s linear;
}

.utility-inner {
  width: 100%;
  max-width: var(--shell);
  height: 100%;
  margin: 0 auto;
  padding: 0 var(--gutter);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
}

.utility-note {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 12px;
  letter-spacing: 0.04em;
  color: rgba(255, 255, 255, 0.72);
}

.utility-dot {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--mint);
  box-shadow: 0 0 0 3px rgba(123, 224, 184, 0.18);
  flex: none;
}

.utility-nav {
  display: flex;
  align-items: center;
  gap: 4px;
}

.utility-link {
  display: inline-flex;
  align-items: center;
  padding: 5px 11px;
  border-radius: 3px;
  font-size: 12.5px;
  font-weight: 700;
  letter-spacing: 0.03em;
  color: rgba(255, 255, 255, 0.82);
  transition: background 0.15s ease, color 0.15s ease;
}

.utility-link:hover {
  color: #FFFFFF;
  background: rgba(255, 255, 255, 0.1);
}

.utility-link--solid {
  background: var(--blue);
  color: #FFFFFF;
}

.utility-link--solid:hover {
  background: var(--blue-deep);
  color: #FFFFFF;
}

.masthead {
  max-width: var(--shell);
  margin: 0 auto;
  padding: clamp(18px, 3vw, 30px) var(--gutter) clamp(14px, 2.4vw, 22px);
}

.masthead-inner {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto minmax(0, 1fr);
  align-items: center;
  gap: 18px;
}

.masthead-meta {
  display: flex;
  align-items: center;
  gap: 8px;
  font-family: var(--font-mono);
  font-size: 11px;
  font-weight: 500;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--muted);
}

.masthead-meta::before {
  content: "";
  width: 26px;
  height: 1px;
  background: var(--line);
  flex: none;
}

.masthead-meta .mono {
  color: var(--ink);
}

.masthead-meta--end {
  justify-content: flex-end;
}

.masthead-meta--end::before {
  display: none;
}

.masthead-meta--end::after {
  content: "";
  width: 26px;
  height: 1px;
  background: var(--line);
  flex: none;
}

.brand {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 7px;
  text-align: center;
  color: var(--ink);
  min-width: 0;
}

.brand-mark {
  font-family: var(--font-display);
  font-weight: 600;
  font-size: clamp(30px, 4.4vw, 44px);
  line-height: 1;
  letter-spacing: 0.18em;
  text-indent: 0.18em;
  color: var(--ink);
  transition: color 0.18s ease;
}

.brand:hover .brand-mark {
  color: var(--blue);
}

.brand-sub {
  font-size: 11px;
  font-weight: 500;
  letter-spacing: 0.2em;
  color: var(--muted);
}

.nav-band {
  background: var(--card);
  border-top: 1px solid var(--ink);
}

.nav-band-inner {
  position: relative;
  max-width: var(--shell);
  margin: 0 auto;
  padding: 0 var(--gutter);
  display: flex;
  align-items: center;
  gap: 12px;
}

.nav-toggle {
  display: none;
  align-items: center;
  gap: 9px;
  margin: 12px 0;
  padding: 10px 14px;
  border: 1px solid var(--line);
  border-radius: 4px;
  background: var(--card);
  color: var(--ink);
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 0.04em;
}

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

.nav-toggle-bars {
  position: relative;
  display: block;
  width: 16px;
  height: 10px;
  flex: none;
}

.nav-toggle-bars::before,
.nav-toggle-bars::after {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  height: 2px;
  background: currentColor;
  transition: top 0.2s ease, transform 0.2s ease;
}

.nav-toggle-bars::before { top: 0; }
.nav-toggle-bars::after { top: 8px; }

.nav-toggle[aria-expanded="true"] .nav-toggle-bars::before {
  top: 4px;
  transform: rotate(45deg);
}

.nav-toggle[aria-expanded="true"] .nav-toggle-bars::after {
  top: 4px;
  transform: rotate(-45deg);
}

.nav-toggle-text {
  line-height: 1;
}

.primary-nav {
  width: 100%;
}

.nav-list {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
}

.nav-link {
  display: inline-flex;
  align-items: center;
  gap: 9px;
  padding: 15px 20px;
  border-bottom: 2px solid transparent;
  font-size: 14px;
  font-weight: 700;
  letter-spacing: 0.01em;
  color: var(--muted);
  transition: color 0.15s ease, border-color 0.15s ease, background 0.15s ease;
}

.nav-link:hover {
  color: var(--ink);
}

.nav-index {
  font-family: var(--font-mono);
  font-size: 10px;
  font-weight: 500;
  letter-spacing: 0.06em;
  color: #A9B2C0;
  transition: color 0.15s ease;
}

.nav-link:hover .nav-index {
  color: var(--blue);
}

.nav-link[aria-current="page"] {
  color: var(--ink);
  border-bottom-color: var(--blue);
}

.nav-link[aria-current="page"] .nav-index {
  color: var(--blue);
}

/* ---------- footer ---------- */
.site-footer {
  margin-top: clamp(40px, 6vw, 96px);
  background: var(--card);
  border-top: 1px solid var(--ink);
  color: var(--ink);
}

.footer-top {
  max-width: var(--shell);
  margin: 0 auto;
  padding: clamp(36px, 5.5vw, 64px) var(--gutter) clamp(28px, 4vw, 48px);
}

.footer-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: 34px 30px;
}

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

.brand--footer {
  align-items: flex-start;
  text-align: left;
  gap: 8px;
}

.brand--footer .brand-mark {
  font-size: 30px;
}

.footer-desc {
  margin-top: 14px;
  max-width: 32ch;
  font-size: 13.5px;
  line-height: 1.8;
  color: var(--muted);
}

.footer-stamp {
  margin-top: 16px;
  padding-top: 12px;
  max-width: 200px;
  border-top: 1px solid var(--line);
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 0.12em;
  color: var(--muted);
}

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

.footer-title {
  margin-bottom: 14px;
  padding-bottom: 10px;
  border-bottom: 1px solid var(--line);
  font-family: var(--font-mono);
  font-size: 11px;
  font-weight: 500;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--muted);
}

.footer-list {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.footer-link {
  font-size: 14px;
  color: var(--ink);
  border-bottom: 1px solid transparent;
  transition: color 0.15s ease, border-color 0.15s ease;
}

.footer-link:hover {
  color: var(--blue);
  border-bottom-color: var(--blue);
}

.footer-link[aria-current="page"] {
  color: var(--blue);
}

.footer-contact-item {
  display: flex;
  flex-direction: column;
  gap: 2px;
}

.footer-contact-label {
  font-family: var(--font-mono);
  font-size: 10.5px;
  letter-spacing: 0.13em;
  color: var(--muted);
}

.footer-contact-value {
  font-size: 13.5px;
  color: var(--ink);
  overflow-wrap: break-word;
}

.footer-note {
  margin-top: 16px;
  max-width: 28ch;
  font-size: 12px;
  line-height: 1.7;
  color: var(--muted);
}

.footer-bottom {
  border-top: 1px solid var(--line);
}

.footer-bottom-inner {
  max-width: var(--shell);
  margin: 0 auto;
  padding: 18px var(--gutter);
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 10px 22px;
  font-family: var(--font-mono);
  font-size: 11.5px;
  letter-spacing: 0.04em;
  color: var(--muted);
}

.footer-copy {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 6px;
}

.footer-icp {
  letter-spacing: 0.06em;
}

.to-top {
  position: fixed;
  right: clamp(14px, 3vw, 28px);
  bottom: clamp(14px, 3vw, 28px);
  z-index: 95;
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 10px 14px;
  border: 1px solid var(--line);
  border-radius: 4px;
  background: var(--card);
  color: var(--ink);
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 0.1em;
  box-shadow: var(--shadow);
  transition: color 0.15s ease, border-color 0.15s ease, transform 0.15s ease;
}

.to-top:hover {
  color: var(--blue);
  border-color: var(--blue);
  transform: translateY(-2px);
}

.to-top[hidden] {
  display: none;
}

/* ---------- data protocols ---------- */
.js [data-reveal] {
  opacity: 0;
  transform: translateY(16px);
  transition: opacity 0.55s ease, transform 0.55s ease;
}

.js [data-reveal][data-revealed="true"] {
  opacity: 1;
  transform: none;
}

[data-toc] a[aria-current] {
  color: var(--blue);
  font-weight: 700;
}

/* ---------- responsive ---------- */
@media (min-width: 620px) {
  .footer-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}

@media (min-width: 1000px) {
  .footer-grid {
    grid-template-columns: minmax(0, 1.6fr) minmax(0, 1fr) minmax(0, 1.1fr) minmax(0, 1fr);
    gap: 30px 36px;
  }
}

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

  .nav-band-inner {
    flex-wrap: wrap;
  }

  .primary-nav {
    position: absolute;
    left: 0;
    right: 0;
    top: 100%;
    z-index: 80;
    display: none;
    padding: 6px 0 10px;
    background: var(--card);
    border-top: 1px solid var(--line);
    border-bottom: 1px solid var(--line);
    box-shadow: 0 24px 36px -30px rgba(17, 24, 39, 0.5);
  }

  .primary-nav[data-open="true"] {
    display: block;
  }

  .nav-list {
    flex-direction: column;
    justify-content: flex-start;
  }

  .nav-item {
    width: 100%;
  }

  .nav-link {
    width: 100%;
    justify-content: space-between;
    padding: 13px var(--gutter);
    border-bottom: 1px solid var(--line);
    border-left: 2px solid transparent;
    color: var(--ink);
  }

  .nav-link[aria-current="page"] {
    background: var(--blue-tint);
    border-left-color: var(--blue);
    border-bottom-color: var(--line);
  }

  .nav-index {
    order: 2;
    font-size: 10.5px;
  }
}

@media (max-width: 720px) {
  .masthead-inner {
    grid-template-columns: minmax(0, 1fr);
    justify-items: center;
    gap: 0;
  }

  .masthead-meta {
    display: none;
  }

  .utility-note {
    display: none;
  }

  .utility-nav {
    width: 100%;
    justify-content: space-between;
  }

  .utility-link {
    padding: 5px 9px;
  }
}

@media (max-width: 400px) {
  .brand-sub {
    letter-spacing: 0.12em;
    font-size: 10.5px;
  }
}

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

  *,
  *::before,
  *::after {
    animation-duration: 0.001ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.001ms !important;
    scroll-behavior: auto !important;
  }

  .js [data-reveal],
  .js [data-reveal][data-revealed="true"] {
    opacity: 1;
    transform: none;
  }
}