.page-about {
  --about-strong: #EDF1F4;
  --about-gap: 64px;
  --about-body: 62ch;
}

/* ---------- 首屏 ---------- */
.page-about .about-hero {
  position: relative;
  padding: 40px 0 8px;
  background-image:
    linear-gradient(var(--line-600) 1px, transparent 1px),
    linear-gradient(90deg, var(--line-600) 1px, transparent 1px);
  background-size: 120px 120px;
  background-position: -1px -1px;
}

.page-about .about-hero::after {
  content: "";
  position: absolute;
  inset: 0;
  pointer-events: none;
  background: radial-gradient(120% 80% at 12% 0%, rgba(200, 162, 74, 0.09), transparent 62%);
}

.page-about .about-hero > .wrap {
  position: relative;
  z-index: 1;
}

.page-about .about-hero__title {
  margin: 14px 0 20px;
  font-size: clamp(2.2rem, 8vw, 4.4rem);
  font-weight: 300;
  line-height: 1.04;
  letter-spacing: -0.02em;
  color: var(--about-strong);
  max-width: 18ch;
}

.page-about .about-hero__lead {
  margin: 0 0 40px;
  max-width: 56ch;
  font-size: 1rem;
  line-height: 1.85;
  color: var(--mist-200);
}

.page-about .hero-facts {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  margin: 0;
  padding: 0;
  list-style: none;
  border-top: 1px solid var(--line-600);
}

.page-about .hero-facts__item {
  display: flex;
  flex-direction: column;
  gap: 6px;
  padding: 18px 0 16px;
  border-bottom: 1px solid var(--line-600);
}

.page-about .hero-facts__item:nth-child(odd) {
  padding-right: 16px;
  border-right: 1px solid var(--line-600);
}

.page-about .hero-facts__item:nth-child(even) {
  padding-left: 16px;
}

.page-about .hero-facts__num {
  font-family: var(--font-mono);
  font-size: 1.5rem;
  font-weight: 600;
  line-height: 1;
  letter-spacing: -0.01em;
  color: var(--gold-500);
  font-variant-numeric: tabular-nums;
}

.page-about .hero-facts__label {
  font-size: 12px;
  letter-spacing: 0.1em;
  color: var(--mist-400);
}

/* ---------- 章节骨架 ---------- */
.page-about .chapter {
  padding: var(--about-gap) 0 0;
}

.page-about .chapter__grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: 24px;
}

.page-about .chapter__axis {
  display: flex;
  align-items: center;
  gap: 12px;
  font-family: var(--font-mono);
  letter-spacing: 0.14em;
}

.page-about .chapter__axis::before {
  content: "";
  flex: none;
  width: 30px;
  height: 1px;
  background: var(--gold-500);
  transition: background-color 300ms var(--ease), width 300ms var(--ease);
}

.page-about .chapter.is-active .chapter__axis::before {
  width: 46px;
  background: var(--magenta-500);
}

.page-about .chapter__num {
  font-size: 13px;
  font-weight: 600;
  color: var(--mist-400);
  font-variant-numeric: tabular-nums;
  transition: color 300ms var(--ease);
}

.page-about .chapter.is-active .chapter__num {
  color: var(--gold-500);
}

.page-about .chapter__label {
  font-size: 11px;
  letter-spacing: 0.24em;
  color: var(--mist-400);
}

.page-about .chapter__title {
  margin: 0 0 20px;
  font-size: clamp(1.45rem, 4.4vw, 2.05rem);
  font-weight: 300;
  line-height: 1.3;
  letter-spacing: -0.01em;
  color: var(--about-strong);
  max-width: 24ch;
}

.page-about .chapter__body p {
  margin: 0 0 16px;
  max-width: var(--about-body);
  font-size: 0.95rem;
  line-height: 1.85;
  color: var(--mist-200);
}

.page-about .chapter__body p:last-child {
  margin-bottom: 0;
}

/* ---------- 旁注 ---------- */
.page-about .chapter__note {
  padding: 2px 0 0 16px;
  border-left: 1px solid var(--line-600);
}

.page-about .chapter__note-title {
  margin: 0 0 12px;
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 0.2em;
  color: var(--jade-400);
}

.page-about .note-list {
  margin: 0;
  padding: 0;
  list-style: none;
  display: grid;
  gap: 8px;
  font-size: 13px;
  line-height: 1.7;
  color: var(--mist-400);
}

.page-about .note-list li {
  position: relative;
  padding-left: 12px;
}

.page-about .note-list li::before {
  content: "";
  position: absolute;
  left: 0;
  top: 0.66em;
  width: 5px;
  height: 1px;
  background: var(--jade-400);
}

.page-about .note-list .num {
  margin-right: 6px;
  color: var(--gold-500);
  font-family: var(--font-mono);
  font-weight: 600;
  font-variant-numeric: tabular-nums;
}

.page-about .note-list--state li::before {
  background: var(--mist-400);
}

.page-about .note-steps {
  margin: 0;
  padding: 0;
  list-style: none;
  display: grid;
  gap: 10px;
  font-size: 13px;
  line-height: 1.6;
  color: var(--mist-200);
}

.page-about .note-steps .num {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 18px;
  height: 18px;
  margin-right: 8px;
  border: 1px solid var(--line-600);
  font-family: var(--font-mono);
  font-size: 11px;
  color: var(--jade-400);
  vertical-align: 1px;
}

.page-about .chapter__note-foot {
  margin: 14px 0 0;
  padding-top: 12px;
  border-top: 1px solid var(--line-600);
  font-size: 12px;
  line-height: 1.7;
  color: var(--mist-400);
}

/* ---------- 图与分栏 ---------- */
.page-about .media {
  margin: 0 0 24px;
}

.page-about .media__img {
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.page-about .chapter__figure {
  margin: 0 0 24px;
}

.page-about .chapter__split {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: 20px;
}

.page-about .chapter__prose p {
  margin: 0 0 16px;
  max-width: var(--about-body);
  font-size: 0.95rem;
  line-height: 1.85;
  color: var(--mist-200);
}

.page-about .chapter__prose p:last-child {
  margin-bottom: 0;
}

/* ---------- 版本线 SVG ---------- */
.page-about .tier-line {
  display: block;
  width: 100%;
  height: auto;
  margin: 4px 0 26px;
  overflow: visible;
}

.page-about .tier-line__axis {
  stroke: var(--line-600);
  stroke-width: 1;
}

.page-about .tier-line__tick {
  stroke: var(--line-600);
  stroke-width: 1;
}

.page-about .tier-line__v1 {
  stroke: var(--mist-400);
  stroke-width: 1;
  opacity: 0.45;
}

.page-about .tier-line__v2 {
  stroke: var(--jade-400);
  stroke-width: 1;
  opacity: 0.6;
}

.page-about .tier-line__v3 {
  stroke: var(--gold-500);
  stroke-width: 2.5;
}

.page-about .tier-line__dot {
  fill: var(--gold-300);
}

.page-about .tier-line__tag {
  font-family: var(--font-mono);
  font-size: 12px;
  letter-spacing: 0.14em;
  fill: var(--mist-400);
}

.page-about .tier-line__tag--live {
  fill: var(--gold-300);
  font-weight: 600;
}

/* ---------- 折叠 ---------- */
.page-about .fold {
  margin-top: 24px;
  border: 1px solid var(--line-600);
  background: var(--ink-700);
}

.page-about .fold__sum {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  padding: 15px 18px;
  cursor: pointer;
  font-family: var(--font-mono);
  font-size: 12px;
  letter-spacing: 0.14em;
  color: var(--jade-400);
  list-style: none;
  transition: color 220ms var(--ease);
}

.page-about .fold__sum::-webkit-details-marker {
  display: none;
}

.page-about .fold__sum::after {
  content: "＋";
  color: var(--mist-400);
  font-size: 13px;
}

.page-about .fold[open] .fold__sum::after {
  content: "－";
  color: var(--magenta-500);
}

.page-about .fold__sum:hover {
  color: var(--gold-300);
}

.page-about .fold__body {
  padding: 4px 18px 18px;
  border-top: 1px solid var(--line-600);
}

.page-about .fold__list {
  margin: 0;
  padding: 0;
  list-style: none;
  display: grid;
  gap: 10px;
}

.page-about .fold__list li {
  position: relative;
  padding-left: 14px;
  font-size: 0.9rem;
  line-height: 1.8;
  color: var(--mist-200);
}

.page-about .fold__list li::before {
  content: "";
  position: absolute;
  left: 0;
  top: 0.75em;
  width: 6px;
  height: 1px;
  background: var(--gold-500);
}

/* ---------- 四象限职能 ---------- */
.page-about .duties {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: 12px;
  margin-top: 4px;
}

.page-about .duty {
  padding: 20px 18px;
  background: var(--ink-800);
  border: 1px solid var(--line-600);
  transition: border-color 240ms var(--ease), box-shadow 240ms var(--ease);
}

.page-about .duty:hover,
.page-about .duty:focus-within {
  border-color: var(--jade-400);
  box-shadow: inset 0 0 0 1px rgba(79, 191, 159, 0.16);
}

.page-about .duty__title {
  display: flex;
  align-items: baseline;
  gap: 10px;
  margin: 0 0 10px;
  font-size: 1rem;
  font-weight: 500;
  letter-spacing: 0.02em;
  color: var(--about-strong);
}

.page-about .duty__idx {
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 0.14em;
  color: var(--gold-500);
}

.page-about .duty__line {
  margin: 0;
  font-size: 13px;
  line-height: 1.75;
  color: var(--mist-400);
}

.page-about .duty__more {
  margin: 0;
  padding-top: 10px;
  font-size: 12px;
  line-height: 1.75;
  color: var(--mist-400);
  opacity: 1;
  max-height: none;
  overflow: visible;
}

/* ---------- 刻度带 ---------- */
.page-about .cadence {
  position: relative;
  height: 56px;
  margin: 26px 0 6px;
}

.page-about .cadence__track {
  position: absolute;
  left: 0;
  right: 0;
  top: 50%;
  height: 1px;
  background: linear-gradient(90deg, var(--line-600), var(--gold-500), var(--jade-400));
  opacity: 0.85;
}

.page-about .cadence__node {
  position: absolute;
  top: 50%;
  width: 1px;
  height: 22px;
  transform: translate(-50%, -50%);
  background: repeating-linear-gradient(180deg, var(--mist-400) 0 3px, transparent 3px 6px);
}

.page-about .cadence__node--year {
  width: 3px;
  height: 38px;
  background: var(--gold-500);
}

.page-about .cadence__node:nth-child(2) { left: 6%; }
.page-about .cadence__node:nth-child(3) { left: 28%; }
.page-about .cadence__node:nth-child(4) { left: 50%; }
.page-about .cadence__node:nth-child(5) { left: 72%; }
.page-about .cadence__node:nth-child(6) { left: 94%; }

.page-about .cadence-legend {
  display: grid;
  gap: 8px;
  margin: 0 0 24px;
  padding: 0;
  list-style: none;
  font-size: 12px;
  line-height: 1.6;
  color: var(--mist-400);
}

.page-about .cadence-legend li {
  display: flex;
  align-items: center;
  gap: 10px;
}

.page-about .cadence-legend__key {
  flex: none;
  width: 22px;
  height: 1px;
}

.page-about .cadence-legend__key--q {
  background: repeating-linear-gradient(90deg, var(--mist-400) 0 3px, transparent 3px 6px);
}

.page-about .cadence-legend__key--y {
  height: 3px;
  background: var(--gold-500);
}

/* ---------- 出口 ---------- */
.page-about .outro {
  margin-top: var(--about-gap);
  padding: 48px 0 56px;
  border-top: 1px solid var(--line-600);
  background: var(--ink-800);
}

.page-about .outro__title {
  margin: 0 0 22px;
  font-size: 11px;
  font-family: var(--font-mono);
  font-weight: 500;
  letter-spacing: 0.24em;
  color: var(--mist-400);
}

.page-about .outro__links {
  margin: 0;
  padding: 0;
  list-style: none;
}

.page-about .outro__links li {
  border-top: 1px solid var(--line-600);
}

.page-about .outro__links li:last-child {
  border-bottom: 1px solid var(--line-600);
}

.page-about .outro__link {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 18px;
  padding: 18px 2px;
  font-size: 0.95rem;
  line-height: 1.6;
  color: var(--mist-200);
  text-decoration: none;
  transition: color 220ms var(--ease);
}

.page-about .outro__mark {
  flex: none;
  font-family: var(--font-mono);
  color: var(--jade-400);
  transition: color 220ms var(--ease), transform 220ms var(--ease);
}

.page-about .outro__link:hover {
  color: var(--gold-300);
}

.page-about .outro__link:hover .outro__mark {
  color: var(--magenta-500);
}

.page-about .outro__link:focus-visible,
.page-about .fold__sum:focus-visible,
.page-about .crumbs__link:focus-visible {
  outline: 2px solid var(--magenta-500);
  outline-offset: 3px;
}

/* ---------- 桌面栅格 ---------- */
@media (min-width: 768px) {
  .page-about .hero-facts {
    grid-template-columns: repeat(3, minmax(0, 1fr));
  }

  .page-about .hero-facts__item {
    padding: 22px 0 20px;
  }

  .page-about .hero-facts__item:nth-child(odd) {
    padding-right: 20px;
    border-right: 0;
  }

  .page-about .hero-facts__item:nth-child(even) {
    padding-left: 0;
  }

  .page-about .hero-facts__item:not(:nth-child(3n)) {
    padding-right: 20px;
    border-right: 1px solid var(--line-600);
  }

  .page-about .hero-facts__item:nth-child(3n) {
    padding-left: 20px;
    border-right: 0;
  }

  .page-about .chapter__split {
    grid-template-columns: minmax(150px, 210px) minmax(0, 1fr);
    gap: 32px;
    align-items: start;
  }

  .page-about .chapter__figure {
    margin-bottom: 0;
  }

  .page-about .cadence-legend {
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 24px;
  }
}

@media (min-width: 1024px) {
  .page-about {
    --about-gap: 92px;
  }

  .page-about .about-hero {
    padding-top: 64px;
  }

  .page-about .hero-facts {
    grid-template-columns: repeat(6, minmax(0, 1fr));
  }

  .page-about .hero-facts__item,
  .page-about .hero-facts__item:nth-child(3n),
  .page-about .hero-facts__item:nth-child(odd),
  .page-about .hero-facts__item:nth-child(even) {
    padding: 24px 18px 22px;
    border-right: 1px solid var(--line-600);
  }

  .page-about .hero-facts__item:first-child {
    padding-left: 0;
  }

  .page-about .hero-facts__item:last-child {
    padding-right: 0;
    border-right: 0;
  }

  .page-about .chapter__grid {
    grid-template-columns: 132px minmax(0, 1fr) 268px;
    gap: 0 40px;
    align-items: start;
  }

  .page-about .chapter__axis {
    position: sticky;
    top: calc(var(--head-h) + 34px);
  }

  .page-about .chapter__note {
    padding-left: 22px;
  }

  .page-about .duties {
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 1px;
    background: var(--line-600);
  }

  .page-about .duty {
    border-color: transparent;
    background: var(--ink-800);
  }

  .page-about .duty:hover,
  .page-about .duty:focus-within {
    border-color: var(--jade-400);
    box-shadow: none;
  }
}

@media (hover: hover) and (min-width: 1024px) {
  .page-about .duty__more {
    max-height: 0;
    padding-top: 0;
    opacity: 0;
    overflow: hidden;
    transition: max-height 320ms var(--ease), opacity 320ms var(--ease), padding-top 320ms var(--ease);
  }

  .page-about .duty:hover .duty__more,
  .page-about .duty:focus-within .duty__more {
    max-height: 140px;
    padding-top: 10px;
    opacity: 1;
  }
}

@media (prefers-reduced-motion: reduce) {
  .page-about .chapter__axis::before,
  .page-about .chapter__num,
  .page-about .duty,
  .page-about .duty__more,
  .page-about .outro__link,
  .page-about .outro__mark {
    transition: none;
  }
}