.page-about {
  --about-rail: 190px;
  --about-gap: 54px;
  background:
    radial-gradient(900px 520px at 88% -8%, rgba(79, 227, 208, .10), transparent 68%),
    radial-gradient(720px 460px at 2% 34%, rgba(122, 46, 67, .16), transparent 72%),
    var(--ink);
  color: var(--silver);
  padding: calc(var(--header-h) + 22px) 0 76px;
  overflow-x: hidden;
}

.page-about .about-hero {
  position: relative;
  padding-bottom: 8px;
}

.page-about .about-hero::after {
  content: "";
  position: absolute;
  right: -8%;
  top: 14%;
  width: 42%;
  height: 1px;
  background: linear-gradient(90deg, transparent, var(--hair-strong));
  transform: rotate(-24deg);
  pointer-events: none;
}

.page-about .about-hero h1 {
  margin: 14px 0 20px;
  max-width: 22ch;
  font-family: var(--font-sans);
  font-weight: 800;
  font-size: clamp(1.9rem, 7.4vw, 3.6rem);
  line-height: 1.14;
  letter-spacing: -.01em;
  color: var(--silver);
}

.page-about .about-hero__lead {
  max-width: 64ch;
  margin: 0;
  font-family: var(--font-serif);
  font-size: 1.0625rem;
  line-height: 1.9;
  color: var(--mist);
}

.page-about .about-hero__facts {
  list-style: none;
  margin: 30px 0 0;
  padding: 0;
  display: grid;
  gap: 1px;
  background: var(--hair);
  border: 1px solid var(--hair);
  border-radius: var(--r-md);
  overflow: hidden;
}

.page-about .about-hero__facts li {
  display: flex;
  align-items: baseline;
  gap: 12px;
  padding: 15px 18px;
  background: rgba(11, 18, 32, .94);
  font-family: var(--font-sans);
  font-size: .88rem;
  line-height: 1.6;
  color: var(--mist);
}

.page-about .about-hero__facts .mono {
  color: var(--signal);
  font-size: .9rem;
  letter-spacing: .06em;
  white-space: nowrap;
}

.page-about .about-body {
  display: block;
  margin-top: 44px;
}

/* 章节索引：移动端横向滑动 */
.page-about .about-rail {
  margin-bottom: 26px;
}

.page-about .about-index {
  list-style: none;
  margin: 12px 0 0;
  padding: 0;
  display: flex;
  gap: 8px;
  overflow-x: auto;
  scrollbar-width: none;
}

.page-about .about-index::-webkit-scrollbar {
  display: none;
}

.page-about .about-index li {
  position: relative;
  flex: 0 0 auto;
}

.page-about .about-index a {
  display: inline-flex;
  align-items: baseline;
  gap: 8px;
  padding: 8px 14px;
  border: 1px solid var(--hair);
  border-radius: 999px;
  color: var(--mist);
  font-family: var(--font-sans);
  font-size: .82rem;
  white-space: nowrap;
  text-decoration: none;
  transition: color .2s var(--ease), border-color .2s var(--ease), background-color .2s var(--ease);
}

.page-about .about-index a .mono {
  font-size: .7rem;
  letter-spacing: .1em;
  color: var(--signal);
}

.page-about .about-index a:hover,
.page-about .about-index a:focus-visible {
  color: var(--silver);
  border-color: rgba(79, 227, 208, .5);
  background: rgba(79, 227, 208, .08);
}

.page-about .about-rail__cta {
  margin-top: 16px;
  width: 100%;
}

/* 章节主体 */
.page-about .chapter {
  position: relative;
  padding: 38px 0 10px;
}

.page-about .chapter + .chapter {
  margin-top: 20px;
}

.page-about .chapter::before {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  top: 0;
  height: 1px;
  background: linear-gradient(90deg, var(--hair-strong), transparent 72%);
  transform: rotate(-.5deg);
  transform-origin: left center;
}

.page-about .chapter__head {
  display: flex;
  align-items: flex-start;
  gap: 14px;
  margin-bottom: 18px;
}

.page-about .chapter__num {
  flex: 0 0 auto;
  padding-top: .5em;
  font-size: .76rem;
  letter-spacing: .12em;
  color: var(--signal);
}

.page-about .chapter__title {
  margin: 0;
  font-family: var(--font-sans);
  font-weight: 800;
  font-size: clamp(1.3rem, 4.6vw, 2rem);
  line-height: 1.22;
  letter-spacing: -.01em;
  color: var(--silver);
}

.page-about .chapter p {
  margin: 0 0 1.05em;
  font-family: var(--font-serif);
  font-size: 1rem;
  line-height: 1.9;
  color: var(--mist);
}

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

.page-about .chapter__link {
  color: var(--signal);
  text-decoration: none;
  border-bottom: 1px solid rgba(79, 227, 208, .35);
  transition: color .2s var(--ease), border-color .2s var(--ease);
}

.page-about .chapter__link:hover,
.page-about .chapter__link:focus-visible {
  color: var(--silver);
  border-color: var(--silver);
}

.page-about .chapter__split {
  display: grid;
  gap: 22px;
}

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

.page-about .chapter__figure img {
  display: block;
  width: 100%;
  height: auto;
  border-radius: var(--r-lg);
  border: 1px solid var(--hair);
  object-fit: cover;
}

.page-about .chapter__figure figcaption {
  margin-top: 10px;
  font-family: var(--font-mono);
  font-size: .72rem;
  letter-spacing: .05em;
  line-height: 1.6;
  color: var(--mist);
}

.page-about .chapter__figure--wide {
  margin-top: 22px;
}

/* 深蓝绿大字引文 */
.page-about .pullquote {
  margin: 26px 0 6px;
  padding: 26px 22px;
  border-radius: var(--r-lg);
  background:
    radial-gradient(120% 140% at 0% 0%, rgba(79, 227, 208, .16), transparent 62%),
    var(--teal-deep);
  border: 1px solid rgba(79, 227, 208, .18);
}

.page-about .pullquote p {
  margin: 0;
  font-family: var(--font-sans);
  font-weight: 700;
  font-size: clamp(1.05rem, 3.8vw, 1.5rem);
  line-height: 1.55;
  letter-spacing: -.005em;
  color: var(--silver);
}

/* 时间线 */
.page-about .timeline {
  position: relative;
  list-style: none;
  margin: 18px 0 0;
  padding: 0 0 0 20px;
}

.page-about .timeline::before {
  content: "";
  position: absolute;
  left: 3px;
  top: 14px;
  bottom: 14px;
  width: 1px;
  background: linear-gradient(180deg, var(--gold), rgba(231, 183, 95, .08));
}

.page-about .timeline > li {
  position: relative;
}

.page-about .timeline > li::before {
  content: "";
  position: absolute;
  left: -20px;
  top: 20px;
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--gold);
  box-shadow: 0 0 0 4px rgba(231, 183, 95, .12);
}

.page-about .tl-item {
  border-bottom: 1px solid var(--hair);
}

.page-about .tl-item:last-child {
  border-bottom: 0;
}

.page-about .tl-item summary {
  list-style: none;
  cursor: pointer;
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  gap: 10px;
  padding: 14px 0;
  font-family: var(--font-sans);
  font-size: .95rem;
  line-height: 1.55;
  color: var(--silver);
  transition: color .2s var(--ease);
}

.page-about .tl-item summary::-webkit-details-marker {
  display: none;
}

.page-about .tl-item summary::after {
  content: "+";
  margin-left: auto;
  font-family: var(--font-mono);
  font-size: 1rem;
  color: var(--gold);
}

.page-about .tl-item[open] summary::after {
  content: "−";
}

.page-about .tl-item summary .mono {
  font-size: .76rem;
  letter-spacing: .1em;
  color: var(--gold);
}

.page-about .tl-item summary:hover,
.page-about .tl-item summary:focus-visible {
  color: var(--signal);
}

.page-about .tl-item p {
  margin: 0 0 16px;
  font-size: .95rem;
  line-height: 1.85;
}

/* 覆盖数字 */
.page-about .coverage {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 12px;
  margin: 20px 0 0;
}

.page-about .coverage__item {
  display: flex;
  flex-direction: column;
  gap: 6px;
  padding: 18px 16px;
  border: 1px solid var(--hair);
  border-radius: var(--r-md);
  background: rgba(27, 27, 58, .46);
}

.page-about .coverage__item--accent {
  background: linear-gradient(150deg, rgba(122, 46, 67, .55), rgba(27, 27, 58, .5));
  border-color: rgba(122, 46, 67, .62);
}

.page-about .coverage__num {
  font-family: var(--font-mono);
  font-size: 1.4rem;
  line-height: 1.1;
  letter-spacing: -.02em;
  color: var(--signal);
}

.page-about .coverage__item--accent .coverage__num {
  color: var(--silver);
}

.page-about .coverage__label {
  font-family: var(--font-sans);
  font-size: .78rem;
  line-height: 1.6;
  color: var(--mist);
}

/* 原则折叠面板 */
.page-about .principles {
  display: grid;
  gap: 10px;
  margin: 20px 0 0;
}

.page-about .principle {
  padding: 0 18px;
  border: 1px solid var(--hair);
  border-radius: var(--r-md);
  background: rgba(15, 46, 46, .42);
  transition: border-color .25s var(--ease), background-color .25s var(--ease);
}

.page-about .principle[open] {
  border-color: rgba(79, 227, 208, .32);
  background: rgba(15, 46, 46, .72);
}

.page-about .principle summary {
  list-style: none;
  cursor: pointer;
  display: flex;
  align-items: baseline;
  gap: 12px;
  padding: 16px 0;
  font-family: var(--font-sans);
  font-weight: 700;
  font-size: .96rem;
  line-height: 1.5;
  color: var(--silver);
}

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

.page-about .principle__num {
  font-size: .72rem;
  letter-spacing: .1em;
  color: var(--gold);
}

.page-about .principle summary:hover,
.page-about .principle summary:focus-visible {
  color: var(--signal);
}

.page-about .principle p {
  margin: 0 0 16px;
  font-size: .93rem;
  line-height: 1.85;
}

/* 下一步 */
.page-about .about-next {
  margin-top: 48px;
  padding: 28px 22px;
  border: 1px solid var(--hair);
  border-radius: var(--r-lg);
  background: linear-gradient(140deg, rgba(27, 27, 58, .78), rgba(11, 18, 32, .92));
}

.page-about .about-next h2 {
  margin: 0 0 10px;
  font-family: var(--font-sans);
  font-weight: 800;
  font-size: clamp(1.2rem, 4vw, 1.6rem);
  line-height: 1.25;
  letter-spacing: -.01em;
  color: var(--silver);
}

.page-about .about-next p {
  margin: 0 0 20px;
  max-width: 58ch;
  font-family: var(--font-serif);
  font-size: .96rem;
  line-height: 1.85;
  color: var(--mist);
}

.page-about .about-next__links {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

/* 断点：平板 */
@media (min-width: 720px) {
  .page-about .about-hero__facts {
    grid-template-columns: repeat(3, minmax(0, 1fr));
  }

  .page-about .coverage {
    grid-template-columns: repeat(4, minmax(0, 1fr));
  }

  .page-about .coverage__item--accent {
    grid-column: span 2;
  }

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

  .page-about .about-next {
    padding: 32px 30px;
  }
}

@media (min-width: 800px) {
  .page-about .chapter__split {
    grid-template-columns: minmax(0, 1.1fr) minmax(0, .9fr);
    gap: 32px;
    align-items: start;
  }

  .page-about .chapter__figure--wide {
    margin-top: 26px;
  }
}

/* 断点：桌面，左窄右宽非对称双栏 */
@media (min-width: 1000px) {
  .page-about {
    padding-top: 38px;
  }

  .page-about .about-body {
    display: grid;
    grid-template-columns: var(--about-rail) minmax(0, 1fr);
    gap: var(--about-gap);
    align-items: start;
    margin-top: 56px;
  }

  .page-about .about-rail {
    position: sticky;
    top: calc(var(--header-h) + 28px);
    margin-bottom: 0;
  }

  .page-about .about-index {
    flex-direction: column;
    gap: 0;
    overflow: visible;
    margin-top: 16px;
  }

  .page-about .about-index li {
    flex: 1 1 auto;
  }

  .page-about .about-index li::before {
    content: "";
    position: absolute;
    left: -3.5px;
    top: 19px;
    width: 7px;
    height: 7px;
    border-radius: 50%;
    background: var(--mist);
    transition: background-color .25s var(--ease), box-shadow .25s var(--ease);
  }

  .page-about .about-index li:hover::before,
  .page-about .about-index li:focus-within::before {
    background: var(--signal);
    box-shadow: 0 0 0 4px rgba(79, 227, 208, .14);
  }

  .page-about .about-index a {
    width: 100%;
    padding: 11px 0 11px 18px;
    border: 0;
    border-left: 1px solid var(--hair);
    border-radius: 0;
    white-space: normal;
    font-size: .86rem;
  }

  .page-about .about-index a:hover,
  .page-about .about-index a:focus-visible {
    background: transparent;
    border-left-color: rgba(79, 227, 208, .55);
  }

  .page-about .about-rail__cta {
    margin-top: 22px;
  }

  .page-about .chapter {
    padding-top: 46px;
  }

  .page-about .chapter + .chapter {
    margin-top: 30px;
  }

  .page-about .pullquote {
    padding: 34px 32px;
  }
}

@media (min-width: 1280px) {
  .page-about {
    --about-rail: 210px;
    --about-gap: 68px;
  }

  .page-about .chapter p {
    font-size: 1.03125rem;
  }
}