.page-about {
  --about-pad: clamp(20px, 5vw, 72px);
  --about-rail-w: 200px;
  --about-line: rgba(53, 242, 214, 0.22);
  --about-line-soft: rgba(53, 242, 214, 0.1);
  background: var(--ink);
  color: var(--dark-ink);
  padding-bottom: clamp(48px, 8vw, 96px);
}

/* ---------- 首屏 ---------- */

.page-about .about-hero {
  position: relative;
  padding: clamp(28px, 5vw, 56px) var(--about-pad) clamp(36px, 6vw, 72px);
  border-bottom: 1px solid var(--about-line);
  overflow: hidden;
}

.page-about .about-hero::after {
  content: "";
  position: absolute;
  right: -12%;
  bottom: -70px;
  width: 62%;
  height: 2px;
  background: linear-gradient(90deg, transparent, var(--cyan));
  transform: rotate(-6deg);
  opacity: 0.55;
  pointer-events: none;
}

.page-about .breadcrumb {
  margin-bottom: clamp(20px, 3vw, 40px);
  position: relative;
  z-index: 1;
}

.page-about .about-hero__kicker {
  margin: 0 0 14px;
  font-family: var(--font-mono);
  font-size: 0.78rem;
  letter-spacing: 0.22em;
  color: var(--mist);
  position: relative;
  z-index: 1;
}

.page-about .about-hero__title {
  margin: 0 0 clamp(20px, 3vw, 32px);
  font-family: var(--font-display);
  font-weight: 900;
  font-size: clamp(2.1rem, 7.4vw, 4.4rem);
  line-height: 1.05;
  letter-spacing: -0.01em;
  color: var(--paper);
  max-width: 16em;
  position: relative;
  z-index: 1;
}

.page-about .about-hero__lede {
  max-width: 40em;
  position: relative;
  z-index: 1;
}

.page-about .about-hero__lede p {
  margin: 0 0 1.1em;
  font-size: clamp(1rem, 2.1vw, 1.125rem);
  line-height: 1.85;
  color: var(--dark-ink);
}

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

.page-about .about-hero__index {
  list-style: none;
  margin: clamp(28px, 4vw, 48px) 0 0;
  padding: 0;
  display: grid;
  grid-template-columns: 1fr;
  gap: 2px;
  max-width: 40em;
  position: relative;
  z-index: 1;
}

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

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

.page-about .about-hero__index a {
  display: flex;
  align-items: baseline;
  gap: 14px;
  padding: 11px 4px;
  color: var(--dark-ink);
  text-decoration: none;
  font-size: 0.98rem;
  letter-spacing: 0.02em;
  transition: color var(--dur) var(--ease), background-color var(--dur) var(--ease);
}

.page-about .about-hero__index a:hover,
.page-about .about-hero__index a:focus-visible {
  color: var(--cyan);
  background: rgba(53, 242, 214, 0.05);
}

.page-about .about-hero__num {
  font-family: var(--font-mono);
  font-size: 0.8rem;
  letter-spacing: 0.08em;
  color: var(--cyan);
  flex: none;
}

/* ---------- 分屏骨架 ---------- */

.page-about .about-split {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: clamp(28px, 5vw, 48px);
  padding: clamp(32px, 5vw, 64px) var(--about-pad) 0;
  align-items: start;
}

/* ---------- 左侧年代刻度 ---------- */

.page-about .about-rail {
  min-width: 0;
}

.page-about .about-rail__label {
  display: none;
  margin: 0 0 20px;
  writing-mode: vertical-rl;
  text-orientation: mixed;
  font-family: var(--font-mono);
  font-size: 0.78rem;
  letter-spacing: 0.3em;
  color: var(--mist);
}

.page-about .about-rail__list {
  list-style: none;
  margin: 0;
  padding: 0 0 4px;
  display: flex;
  gap: 8px;
  overflow-x: auto;
  scrollbar-width: thin;
}

.page-about .about-rail__item {
  flex: none;
}

.page-about .about-rail__link {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 9px 14px;
  border: 1px solid var(--turf);
  background: var(--deep);
  text-decoration: none;
  color: var(--dark-ink);
  white-space: nowrap;
  clip-path: polygon(0 0, calc(100% - 10px) 0, 100% 10px, 100% 100%, 0 100%);
  transition: border-color var(--dur) var(--ease), color var(--dur) var(--ease), background-color var(--dur) var(--ease);
}

.page-about .about-rail__link:hover,
.page-about .about-rail__link:focus-visible {
  border-color: var(--cyan);
  color: var(--cyan);
  background: var(--stand);
}

.page-about .about-rail__vol {
  font-family: var(--font-mono);
  font-size: 0.72rem;
  letter-spacing: 0.1em;
  color: var(--cyan);
}

.page-about .about-rail__era {
  font-size: 0.88rem;
  letter-spacing: 0.04em;
}

.page-about .about-rail__note {
  margin: 14px 0 0;
  font-size: 0.78rem;
  line-height: 1.7;
  color: var(--mist);
  max-width: 20em;
}

/* ---------- 右侧章节流 ---------- */

.page-about .about-flow {
  min-width: 0;
  display: flex;
  flex-direction: column;
  gap: clamp(34px, 5vw, 60px);
}

.page-about .about-chapter {
  border-top: 1px solid var(--about-line);
  padding-top: clamp(18px, 2.6vw, 26px);
}

.page-about .about-chapter__head {
  display: flex;
  align-items: baseline;
  gap: clamp(12px, 2vw, 20px);
  cursor: pointer;
  list-style: none;
  padding: 4px 0 14px;
}

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

.page-about .about-chapter__head:focus-visible {
  outline: 2px solid var(--cyan);
  outline-offset: 4px;
}

.page-about .about-chapter__num {
  font-family: var(--font-mono);
  font-size: clamp(1.9rem, 4.6vw, 3rem);
  line-height: 1;
  letter-spacing: 0.02em;
  color: var(--cyan);
  flex: none;
}

@supports (-webkit-text-stroke: 1px currentColor) {
  .page-about .about-chapter__num {
    color: transparent;
    -webkit-text-stroke: 1px var(--cyan);
  }
  .page-about .about-chapter[open] .about-chapter__head:hover .about-chapter__num {
    color: var(--cyan);
  }
}

.page-about .about-chapter__title {
  margin: 0;
  font-family: var(--font-display);
  font-weight: 900;
  font-size: clamp(1.4rem, 3.6vw, 2rem);
  line-height: 1.2;
  color: var(--paper);
  letter-spacing: -0.005em;
  flex: 1 1 auto;
  min-width: 0;
}

.page-about .about-chapter__toggle {
  flex: none;
  width: 22px;
  height: 22px;
  position: relative;
  align-self: center;
}

.page-about .about-chapter__toggle::before,
.page-about .about-chapter__toggle::after {
  content: "";
  position: absolute;
  background: var(--cyan);
  transition: transform var(--dur) var(--ease), opacity var(--dur) var(--ease);
}

.page-about .about-chapter__toggle::before {
  left: 3px;
  right: 3px;
  top: 50%;
  height: 1px;
  margin-top: -0.5px;
}

.page-about .about-chapter__toggle::after {
  top: 3px;
  bottom: 3px;
  left: 50%;
  width: 1px;
  margin-left: -0.5px;
}

.page-about .about-chapter[open] .about-chapter__toggle::after {
  transform: scaleY(0);
  opacity: 0;
}

.page-about .about-chapter__content {
  padding-top: 2px;
}

.page-about .about-chapter__abstract {
  margin: 0 0 12px;
  font-size: clamp(1.02rem, 2.3vw, 1.2rem);
  line-height: 1.7;
  color: var(--mist);
  max-width: 34em;
}

.page-about .about-chapter__evidence {
  margin: 0 0 clamp(20px, 3vw, 30px);
  padding: 8px 0;
  font-family: var(--font-mono);
  font-size: 0.76rem;
  letter-spacing: 0.06em;
  color: var(--mist);
  border-top: 1px solid var(--cyan);
  border-bottom: 1px solid var(--about-line-soft);
  max-width: 40em;
}

.page-about .about-chapter__body {
  max-width: 36em;
  font-size: 1.0625rem;
  line-height: 1.85;
  color: var(--dark-ink);
}

.page-about .about-chapter__body p {
  margin: 0 0 1.15em;
}

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

.page-about .about-chapter__body-lead {
  color: var(--mist);
}

/* ---------- 内容边界列表 ---------- */

.page-about .about-limits {
  list-style: none;
  margin: 0;
  padding: 0;
  border-top: 1px solid var(--about-line-soft);
}

.page-about .about-limits li {
  padding: 16px 0;
  border-bottom: 1px solid var(--about-line-soft);
}

.page-about .about-limits__key {
  display: block;
  margin-bottom: 6px;
  font-family: var(--font-mono);
  font-size: 0.78rem;
  letter-spacing: 0.16em;
  color: var(--signal);
}

.page-about .about-limits p {
  margin: 0;
  font-size: 1rem;
  line-height: 1.8;
  color: var(--dark-ink);
}

/* ---------- 纸白流程面板 ---------- */

.page-about .about-paper {
  margin: 0 0 clamp(24px, 3.4vw, 36px);
  padding: clamp(22px, 3.4vw, 40px);
  background: var(--paper);
  color: var(--paper-ink);
  clip-path: polygon(0 0, 100% 0, 100% calc(100% - 28px), calc(100% - 28px) 100%, 0 100%);
}

.page-about .about-steps {
  list-style: none;
  margin: 0;
  padding: 0;
  counter-reset: none;
}

.page-about .about-steps li {
  display: flex;
  gap: 16px;
  padding: 16px 0;
  border-bottom: 1px solid var(--paper-line);
}

.page-about .about-steps li:first-child {
  padding-top: 0;
}

.page-about .about-steps li:last-child {
  padding-bottom: 0;
  border-bottom: 0;
}

.page-about .about-steps__no {
  flex: none;
  font-family: var(--font-mono);
  font-size: 0.82rem;
  letter-spacing: 0.08em;
  color: var(--turf);
  padding-top: 3px;
}

.page-about .about-steps__name {
  margin: 0 0 5px;
  font-size: 1rem;
  font-weight: 700;
  color: var(--stand);
  letter-spacing: 0.02em;
}

.page-about .about-steps li p {
  margin: 0;
  font-size: 0.95rem;
  line-height: 1.8;
  color: var(--paper-ink);
}

/* ---------- 图片 ---------- */

.page-about .about-figure {
  margin: 0 0 clamp(22px, 3.2vw, 34px);
}

.page-about .about-figure img {
  display: block;
  width: 100%;
  max-width: 100%;
  height: auto;
  object-fit: cover;
  filter: saturate(0.7) brightness(0.82);
  border: 1px solid var(--turf);
}

.page-about .about-figure--wide img {
  aspect-ratio: 14 / 9;
}

.page-about .about-figure--tall img {
  aspect-ratio: 10 / 14;
}

.page-about .about-figure--square img {
  aspect-ratio: 3 / 2;
}

.page-about .about-figure figcaption {
  margin-top: 9px;
  font-size: 0.76rem;
  line-height: 1.7;
  color: var(--mist);
  letter-spacing: 0.02em;
}

/* ---------- 年代卷 ---------- */

.page-about .about-era-layout {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: clamp(22px, 3.4vw, 36px);
  margin-top: clamp(18px, 2.6vw, 28px);
  align-items: start;
}

.page-about .about-eras {
  list-style: none;
  margin: 0;
  padding: 0;
  border-left: 1px solid var(--turf);
}

.page-about .about-eras__item {
  position: relative;
  padding: 0 0 22px 22px;
}

.page-about .about-eras__item:last-child {
  padding-bottom: 0;
}

.page-about .about-eras__item::before {
  content: "";
  position: absolute;
  left: -4px;
  top: 7px;
  width: 7px;
  height: 7px;
  background: var(--ink);
  border: 1px solid var(--cyan);
  border-radius: 50%;
}

.page-about .about-eras__vol {
  display: block;
  font-family: var(--font-mono);
  font-size: 0.74rem;
  letter-spacing: 0.14em;
  color: var(--cyan);
  margin-bottom: 4px;
}

.page-about .about-eras__name {
  margin: 0 0 6px;
  font-size: 1.06rem;
  font-weight: 700;
  color: var(--paper);
  letter-spacing: 0.02em;
}

.page-about .about-eras__item p {
  margin: 0;
  font-size: 0.94rem;
  line-height: 1.8;
  color: var(--dark-ink);
}

.page-about .about-eras__item:target::before {
  background: var(--cyan);
  box-shadow: 0 0 0 4px rgba(53, 242, 214, 0.16);
}

/* ---------- 术语卡 ---------- */

.page-about .about-terms {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: 12px;
  margin: 0 0 clamp(28px, 4vw, 44px);
}

.page-about .about-term {
  background: var(--stand);
  border-left: 1px solid var(--turf);
  clip-path: polygon(0 0, calc(100% - var(--cut)) 0, 100% var(--cut), 100% 100%, 0 100%);
  padding: 15px 18px;
  transition: background-color var(--dur) var(--ease);
}

.page-about .about-term[open],
.page-about .about-term:hover {
  background: var(--turf);
}

.page-about .about-term .term-card__term {
  cursor: pointer;
  list-style: none;
  font-size: 0.98rem;
  font-weight: 700;
  letter-spacing: 0.04em;
  color: var(--paper);
}

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

.page-about .about-term .term-card__term:focus-visible {
  outline: 2px solid var(--cyan);
  outline-offset: 3px;
}

.page-about .about-term .term-card__def {
  margin: 10px 0 0;
  font-size: 0.9rem;
  line-height: 1.75;
  color: var(--dark-ink);
}

.page-about .about-term .term-card__pages {
  margin: 8px 0 0;
  font-family: var(--font-mono);
  font-size: 0.72rem;
  letter-spacing: 0.04em;
  line-height: 1.7;
  color: var(--mist);
}

.page-about .about-term .term-card__pages a {
  color: var(--cyan);
  text-decoration: underline;
  text-underline-offset: 3px;
}

/* ---------- 延伸阅读 ---------- */

.page-about .about-readmore {
  border-top: 1px solid var(--about-line);
  padding-top: clamp(18px, 2.6vw, 26px);
}

.page-about .about-readmore__title {
  margin: 0 0 14px;
  font-size: 1.02rem;
  font-weight: 700;
  letter-spacing: 0.04em;
  color: var(--paper);
}

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

.page-about .about-readmore__list li {
  padding: 10px 0;
  border-bottom: 1px solid var(--about-line-soft);
  font-size: 0.94rem;
  line-height: 1.75;
  color: var(--dark-ink);
}

.page-about .about-readmore__list li:last-child {
  border-bottom: 0;
}

.page-about .about-readmore__list a {
  color: var(--cyan);
  text-decoration: underline;
  text-underline-offset: 3px;
  margin-right: 4px;
}

.page-about .about-readmore__list a:hover,
.page-about .about-readmore__list a:focus-visible {
  color: var(--mist);
}

/* ---------- 平板 ---------- */

@media (min-width: 640px) {
  .page-about .about-hero__index {
    grid-template-columns: repeat(2, minmax(0, 1fr));
    column-gap: 28px;
  }

  .page-about .about-hero__index li:nth-last-child(-n + 1) {
    border-bottom: 1px solid var(--about-line-soft);
  }

  .page-about .about-terms {
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 14px;
  }

  .page-about .about-rail__list {
    flex-wrap: wrap;
    overflow-x: visible;
  }
}

/* ---------- 桌面：左轨道 + 右章节 ---------- */

@media (min-width: 960px) {
  .page-about .about-split {
    grid-template-columns: var(--about-rail-w) minmax(0, 1fr);
    gap: clamp(36px, 5vw, 88px);
  }

  .page-about .about-rail {
    position: sticky;
    top: 48px;
  }

  .page-about .about-rail__label {
    display: block;
  }

  .page-about .about-rail__list {
    flex-direction: column;
    flex-wrap: nowrap;
    overflow: visible;
    gap: 0;
    position: relative;
    padding-left: 18px;
  }

  .page-about .about-rail__list::before {
    content: "";
    position: absolute;
    left: 3px;
    top: 12px;
    bottom: 12px;
    width: 1px;
    background: var(--turf);
  }

  .page-about .about-rail__item {
    position: relative;
  }

  .page-about .about-rail__item::before {
    content: "";
    position: absolute;
    left: -18px;
    top: 50%;
    width: 7px;
    height: 7px;
    margin-top: -3.5px;
    background: var(--ink);
    border: 1px solid var(--turf);
    border-radius: 50%;
    transition: border-color var(--dur) var(--ease), background-color var(--dur) var(--ease);
  }

  .page-about .about-rail__item:hover::before {
    border-color: var(--cyan);
    background: var(--cyan);
  }

  .page-about .about-rail__link {
    background: transparent;
    border: 0;
    clip-path: none;
    padding: 10px 0;
    flex-direction: column;
    align-items: flex-start;
    gap: 2px;
  }

  .page-about .about-rail__link:hover,
  .page-about .about-rail__link:focus-visible {
    background: transparent;
  }

  .page-about .about-era-layout {
    grid-template-columns: minmax(0, 0.58fr) minmax(0, 1fr);
  }

  .page-about .about-chapter__evidence {
    font-size: 0.78rem;
  }
}

/* ---------- 宽屏 ---------- */

@media (min-width: 1280px) {
  .page-about .about-terms {
    grid-template-columns: repeat(3, minmax(0, 1fr));
  }

  .page-about .about-chapter__body {
    max-width: 38em;
  }
}

/* ---------- 减弱动效 ---------- */

@media (prefers-reduced-motion: reduce) {
  .page-about *,
  .page-about *::before,
  .page-about *::after {
    transition-duration: 0.01ms !important;
    animation-duration: 0.01ms !important;
  }
}
<<<END>>>