.page-about {
  --about-gutter: 1.25rem;
  --about-rule: rgba(14, 27, 42, 0.16);
  --about-muted: #4b5b6b;
  background: var(--warm);
  color: var(--ink);
  font-family: var(--font-sans);
  line-height: 1.75;
  overflow-x: clip;
}

.page-about .about-shell {
  max-width: var(--content-max);
  margin-inline: auto;
  padding: 0 var(--about-gutter) 3.5rem;
}

/* 面包屑 */
.page-about .about-crumb {
  padding-top: var(--about-gutter);
}

.page-about .about-crumb__list {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  margin: 0;
  padding: 0;
  list-style: none;
  font-family: var(--font-mono);
  font-size: 0.75rem;
  letter-spacing: 0.04em;
}

.page-about .about-crumb__list .breadcrumb__item + .breadcrumb__item::before {
  content: "/";
  margin-right: 0.4rem;
  color: var(--slate);
}

.page-about .about-crumb__list .breadcrumb__link {
  color: var(--about-muted);
  text-decoration: none;
}

.page-about .about-crumb__list .breadcrumb__link:hover {
  color: var(--red);
  text-decoration: underline;
  text-underline-offset: 3px;
}

/* 首屏框景 */
.page-about .about-hero {
  position: relative;
  margin-top: 1rem;
  padding: clamp(1.5rem, 5vw, 3.5rem);
  background: var(--ink);
  color: var(--warm);
  display: grid;
  gap: 1.1rem;
  overflow: hidden;
  isolation: isolate;
}

.page-about .about-hero::before {
  content: "";
  position: absolute;
  inset: 0 auto 0 0;
  width: 3px;
  background: var(--red);
  z-index: 2;
}

.page-about .about-hero::after {
  content: "";
  position: absolute;
  top: 0;
  right: 0;
  width: 42%;
  height: 100%;
  background-image: linear-gradient(to right, rgba(143, 163, 181, 0.16) 1px, transparent 1px);
  background-size: 2.2rem 100%;
  pointer-events: none;
  z-index: 1;
}

.page-about .about-hero > * {
  position: relative;
  z-index: 2;
}

.page-about .about-hero__eyebrow {
  margin: 0;
  font-family: var(--font-mono);
  font-size: 0.75rem;
  letter-spacing: 0.16em;
  color: var(--gold);
}

.page-about .about-hero__title {
  margin: 0;
  font-size: clamp(1.75rem, 6vw, 3.4rem);
  line-height: 1.1;
  font-weight: 800;
  letter-spacing: -0.01em;
  max-width: 20ch;
  overflow-wrap: anywhere;
}

.page-about .about-hero__lead {
  margin: 0;
  max-width: 46ch;
  font-size: 1rem;
  color: rgba(243, 235, 221, 0.86);
}

.page-about .about-hero__anchors {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 1.1rem 1rem;
  margin: 0.4rem 0 0;
  padding: 1.25rem 0 0;
  list-style: none;
  border-top: 1px solid var(--line-strong);
}

.page-about .about-anchor__num {
  display: block;
  font-family: var(--font-mono);
  font-size: clamp(1.5rem, 5vw, 2.3rem);
  font-weight: 600;
  line-height: 1;
  letter-spacing: -0.02em;
  color: var(--gold);
}

.page-about .about-anchor__label {
  display: block;
  margin-top: 0.45rem;
  font-size: 0.8125rem;
  line-height: 1.5;
  color: var(--slate);
}

/* 章节索引 */
.page-about .about-index {
  display: flex;
  gap: 0.5rem;
  margin: 0;
  padding: 1rem 0;
  overflow-x: auto;
  border-bottom: 1px solid var(--about-rule);
  scrollbar-width: thin;
}

.page-about .about-index .anchor-index__link {
  flex: 0 0 auto;
  padding: 0.35rem 0.65rem;
  border: 1px solid var(--about-rule);
  font-family: var(--font-mono);
  font-size: 0.75rem;
  letter-spacing: 0.02em;
  color: var(--ink);
  text-decoration: none;
  white-space: nowrap;
  transition: background-color 180ms ease, color 180ms ease, border-color 180ms ease;
}

.page-about .about-index .anchor-index__link:hover,
.page-about .about-index .anchor-index__link:focus-visible {
  border-color: var(--red);
  color: var(--red);
}

.page-about .about-index .anchor-index__link[aria-current] {
  background: var(--ink);
  border-color: var(--ink);
  color: var(--warm);
}

/* 章节流 */
.page-about .about-flow {
  display: grid;
}

.page-about .about-chapter {
  display: grid;
  grid-template-columns: 1fr;
  gap: 0.85rem;
  padding: 2rem 0;
  border-bottom: 1px solid var(--about-rule);
  scroll-margin-top: 4.5rem;
}

.page-about .about-chapter--last {
  border-bottom: 0;
  padding-bottom: 0.5rem;
}

.page-about .about-chapter__marker {
  display: flex;
  align-items: baseline;
  gap: 0.7rem;
}

.page-about .about-chapter__num {
  font-family: var(--font-mono);
  font-size: clamp(2rem, 8vw, 3.2rem);
  font-weight: 600;
  line-height: 1;
  letter-spacing: -0.03em;
  color: var(--red);
}

.page-about .about-chapter__tag {
  font-family: var(--font-mono);
  font-size: 0.6875rem;
  letter-spacing: 0.2em;
  color: var(--slate);
}

.page-about .about-chapter__title {
  margin: 0 0 0.85rem;
  font-size: clamp(1.3rem, 4.4vw, 2rem);
  line-height: 1.25;
  font-weight: 700;
  letter-spacing: -0.01em;
  max-width: 24ch;
}

.page-about .about-chapter__body p {
  margin: 0 0 0.9rem;
  max-width: 60ch;
  font-size: 1rem;
  overflow-wrap: anywhere;
}

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

/* 注释栏 */
.page-about .about-note {
  margin-top: 1.25rem !important;
  padding: 0.4rem 0 0.4rem 1rem;
  border-left: 2px solid var(--red);
  font-size: 0.875rem;
  line-height: 1.7;
  color: var(--about-muted);
  max-width: 46ch;
}

/* 图片框 */
.page-about .about-figure {
  margin: 1.5rem 0 0;
  padding: 0.6rem;
  background: var(--paper);
  border: 1px solid var(--about-rule);
}

.page-about .about-figure img {
  display: block;
  width: 100%;
  max-width: 100%;
  height: auto;
  object-fit: cover;
}

.page-about .about-figure--square {
  max-width: 26rem;
}

.page-about .about-figure figcaption {
  margin-top: 0.55rem;
  padding: 0.5rem 0.15rem 0.1rem;
  border-top: 1px solid var(--about-rule);
  font-family: var(--font-mono);
  font-size: 0.75rem;
  letter-spacing: 0.02em;
  color: var(--about-muted);
}

/* 编号结构图 */
.page-about .about-diagram-wrap {
  margin: 1.5rem 0 0;
  padding: 0.75rem 0.75rem 0.25rem;
  background: var(--ink);
  border: 1px solid var(--line-strong);
}

.page-about .about-diagram {
  display: block;
  width: 100%;
  height: auto;
}

/* 四条内容线 */
.page-about .about-matrix {
  margin: 1.5rem 0 0;
  padding: 0;
  list-style: none;
  border-top: 1px solid var(--about-rule);
}

.page-about .about-matrix__item {
  display: grid;
  grid-template-columns: 2rem minmax(0, 1fr);
  gap: 0.1rem 0.6rem;
  padding: 1rem 0;
  border-bottom: 1px solid var(--about-rule);
}

.page-about .about-matrix__num {
  grid-row: 1 / span 2;
  padding-top: 0.2rem;
  font-family: var(--font-mono);
  font-size: 0.8125rem;
  font-weight: 600;
  color: var(--red);
  transition: color 180ms ease;
}

.page-about .about-matrix__title {
  margin: 0;
  font-size: 1.0625rem;
  font-weight: 700;
  line-height: 1.45;
  transition: color 180ms ease;
}

.page-about .about-matrix__text {
  margin: 0 !important;
  font-size: 0.9375rem;
  line-height: 1.7;
  color: var(--about-muted);
  max-width: 48ch;
}

.page-about .about-matrix__item:hover .about-matrix__title,
.page-about .about-matrix__item:focus-within .about-matrix__title {
  color: var(--red-dark);
}

.page-about .about-matrix__item:hover .about-matrix__num,
.page-about .about-matrix__item:focus-within .about-matrix__num {
  color: var(--ink);
}

/* 出口链接 */
.page-about .about-links {
  margin: 1.4rem 0 0;
  padding: 0;
  list-style: none;
  border-top: 1px solid var(--about-rule);
}

.page-about .about-links__link {
  display: grid;
  gap: 0.15rem;
  padding: 0.9rem 0.25rem 0.9rem 0;
  border-bottom: 1px solid var(--about-rule);
  color: var(--ink);
  text-decoration: none;
  transition: color 180ms ease, padding-left 180ms ease;
}

.page-about .about-links__link strong {
  font-size: 1rem;
  font-weight: 700;
}

.page-about .about-links__link span {
  font-size: 0.875rem;
  line-height: 1.6;
  color: var(--about-muted);
}

.page-about .about-links__link:hover,
.page-about .about-links__link:focus-visible {
  color: var(--red);
  padding-left: 0.4rem;
}

.page-about .about-links__link:hover span,
.page-about .about-links__link:focus-visible span {
  color: var(--about-muted);
}

/* 焦点可见性 */
.page-about a:focus-visible {
  outline: 2px solid var(--red);
  outline-offset: 2px;
}

/* 平板及桌面 */
@media (min-width: 56rem) {
  .page-about {
    --about-gutter: 2.5rem;
  }

  .page-about .about-chapter {
    grid-template-columns: 9.5rem minmax(0, 1fr);
    gap: 2.5rem;
    padding: 3rem 0;
    scroll-margin-top: 5rem;
  }

  .page-about .about-chapter__marker {
    flex-direction: column;
    align-items: flex-start;
    gap: 0.35rem;
    position: sticky;
    top: 4.5rem;
    align-self: start;
  }

  .page-about .about-chapter__tag {
    padding-left: 0.15rem;
  }

  .page-about .about-flow {
    margin-top: 0.5rem;
  }
}

@media (min-width: 64rem) {
  .page-about .about-hero {
    grid-template-columns: minmax(0, 1.15fr) minmax(0, 0.85fr);
    grid-template-areas:
      "eyebrow eyebrow"
      "title anchors"
      "lead anchors";
    align-items: start;
    column-gap: 3.5rem;
    row-gap: 1rem;
  }

  .page-about .about-hero__eyebrow {
    grid-area: eyebrow;
  }

  .page-about .about-hero__title {
    grid-area: title;
  }

  .page-about .about-hero__lead {
    grid-area: lead;
  }

  .page-about .about-hero__anchors {
    grid-area: anchors;
    margin-top: 0;
    padding-top: 0;
    border-top: 0;
    border-left: 1px solid var(--line-strong);
    padding-left: 1.75rem;
  }

  .page-about .about-chapter {
    grid-template-columns: 12rem minmax(0, 1fr);
    gap: 3.5rem;
  }
}

@media (prefers-reduced-motion: reduce) {
  .page-about .about-links__link,
  .page-about .about-matrix__num,
  .page-about .about-matrix__title,
  .page-about .about-index .anchor-index__link {
    transition: none;
  }
}