.page-about {
  --about-rail-w: 208px;
  background: var(--yb-paper);
  color: var(--yb-ink);
  overflow-x: clip;
}

/* ---------- 首屏框景 ---------- */
.page-about .about-hero {
  padding: clamp(18px, 4vw, 40px) 0 clamp(28px, 5vw, 64px);
}

.page-about .about-hero__inner {
  position: relative;
  border: 1px solid var(--yb-line);
  padding: clamp(18px, 3.4vw, 46px);
  background: linear-gradient(180deg, #ffffff 0%, var(--yb-paper) 100%);
}

.page-about .about-hero__inner::before,
.page-about .about-hero__inner::after {
  content: "";
  position: absolute;
  width: 20px;
  height: 20px;
  border: 2px solid var(--yb-blue);
  pointer-events: none;
}

.page-about .about-hero__inner::before {
  top: -2px;
  left: -2px;
  border-right: 0;
  border-bottom: 0;
}

.page-about .about-hero__inner::after {
  right: -2px;
  bottom: -2px;
  border-top: 0;
  border-left: 0;
}

.page-about .about-hero__grid {
  display: grid;
  gap: clamp(24px, 4vw, 56px);
  margin-top: clamp(22px, 3.4vw, 42px);
  align-items: end;
}

.page-about .about-hero__title {
  margin: 14px 0 0;
  font-family: var(--yb-font-sans);
  font-weight: 900;
  font-size: clamp(30px, 6.4vw, 66px);
  line-height: 1.08;
  letter-spacing: 0.02em;
  max-width: 15em;
}

.page-about .about-hero__lede {
  margin: clamp(16px, 2.4vw, 26px) 0 0;
  max-width: 40em;
  font-family: var(--yb-font-serif);
  font-size: 17px;
  line-height: 1.9;
  color: var(--yb-graphite);
}

.page-about .about-hero__facts {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 1px;
  margin: 0;
  background: var(--yb-line);
  border: 1px solid var(--yb-line);
}

.page-about .about-fact {
  background: #ffffff;
  padding: clamp(12px, 2vw, 20px);
  display: flex;
  flex-direction: column-reverse;
  gap: 6px;
  border-top: 3px solid transparent;
}

.page-about .about-fact:nth-child(odd) {
  border-top-color: var(--yb-signal);
}

.page-about .about-fact:nth-child(even) {
  border-top-color: var(--yb-blue);
}

.page-about .about-fact__num {
  margin: 0;
  font-family: var(--yb-font-mono);
  font-weight: 700;
  font-size: clamp(24px, 3.6vw, 34px);
  letter-spacing: 0.04em;
  color: var(--yb-blue-deep);
  line-height: 1;
}

.page-about .about-fact__num span {
  font-size: 0.5em;
  margin-left: 2px;
  color: var(--yb-graphite);
}

.page-about .about-fact__label {
  font-family: var(--yb-font-sans);
  font-size: 12px;
  letter-spacing: 0.08em;
  color: var(--yb-graphite);
  line-height: 1.5;
}

/* ---------- 起点与缘由 ---------- */
.page-about .about-origin {
  padding: clamp(32px, 6vw, 88px) 0;
}

.page-about .about-origin__grid {
  display: grid;
  gap: clamp(24px, 4vw, 56px);
  align-items: start;
}

.page-about .about-origin__text .yb-h2 {
  margin-top: 14px;
}

.page-about .about-origin__text p {
  font-family: var(--yb-font-serif);
  font-size: 17px;
  line-height: 1.9;
  color: var(--yb-graphite);
}

.page-about .about-origin__text p:first-of-type::first-letter {
  font-family: var(--yb-font-sans);
  font-weight: 900;
  font-size: 2.4em;
  line-height: 1;
  float: left;
  margin: 4px 10px 0 0;
  color: var(--yb-blue);
}

.page-about .about-shot {
  margin: 0;
  border: 1px solid var(--yb-line);
  background: var(--yb-glass);
  overflow: hidden;
}

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

.page-about .about-shot__caption {
  display: block;
  padding: 10px 14px;
  font-family: var(--yb-font-sans);
  font-size: 13px;
  letter-spacing: 0.06em;
  color: var(--yb-graphite);
  background: #ffffff;
  border-top: 1px solid var(--yb-line);
}

/* ---------- 时间线区 ---------- */
.page-about .about-track-section {
  padding: clamp(28px, 5vw, 72px) 0 clamp(32px, 6vw, 88px);
  background: linear-gradient(180deg, var(--yb-glass) 0%, var(--yb-paper) 62%);
  border-top: 1px solid var(--yb-line);
}

.page-about .about-track-head {
  max-width: 46em;
}

.page-about .about-track-head .yb-h2 {
  margin-top: 12px;
}

.page-about .about-track-head__lede {
  margin: 14px 0 0;
  font-family: var(--yb-font-serif);
  font-size: 16px;
  line-height: 1.85;
  color: var(--yb-graphite);
}

.page-about .about-band {
  margin: clamp(20px, 3vw, 34px) 0 clamp(24px, 4vw, 44px);
  border: 1px solid var(--yb-line);
  background: var(--yb-blue-deep);
  overflow: hidden;
}

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

.page-about .about-track {
  display: grid;
  gap: clamp(18px, 3vw, 32px);
  align-items: start;
}

.page-about .about-rail__title {
  margin: 0 0 10px;
  font-family: var(--yb-font-mono);
  font-size: 12px;
  letter-spacing: 0.14em;
  color: var(--yb-signal-deep);
  text-transform: uppercase;
}

.page-about .about-rail__list {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  gap: 2px;
}

.page-about .about-rail__link {
  display: flex;
  align-items: baseline;
  gap: 10px;
  padding: 10px 12px 10px 14px;
  border-left: 2px solid var(--yb-line);
  color: var(--yb-graphite);
  text-decoration: none;
  font-family: var(--yb-font-sans);
  font-size: 14px;
  line-height: 1.4;
  transition: color 0.18s var(--yb-ease), border-color 0.18s var(--yb-ease), background-color 0.18s var(--yb-ease);
}

.page-about .about-rail__link:hover {
  color: var(--yb-blue);
  border-left-color: var(--yb-blue);
  background: #ffffff;
}

.page-about .about-rail__link[aria-current="true"] {
  color: var(--yb-blue-deep);
  border-left-color: var(--yb-blue);
  background: #ffffff;
  font-weight: 700;
}

.page-about .about-rail__num {
  font-family: var(--yb-font-mono);
  font-size: 12px;
  letter-spacing: 0.08em;
  color: var(--yb-signal-deep);
}

.page-about .about-stages {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  gap: clamp(14px, 2.2vw, 26px);
}

.page-about .about-stage {
  width: 100%;
  box-sizing: border-box;
  padding: clamp(16px, 2.6vw, 32px);
  background: #ffffff;
  border: 1px solid var(--yb-line);
  border-left: 4px solid var(--yb-blue);
  border-radius: var(--yb-radius);
  transition: transform 0.16s var(--yb-ease), border-color 0.16s var(--yb-ease), box-shadow 0.16s var(--yb-ease);
}

.page-about .about-stage:hover {
  transform: translateY(-2px);
  border-color: var(--yb-blue);
  box-shadow: 0 10px 26px rgba(16, 24, 40, 0.06);
}

.page-about .about-stage--s2 {
  background: var(--yb-glass);
}

.page-about .about-stage--s4 {
  background: var(--yb-sand);
}

.page-about .about-stage--key {
  border-left-color: var(--yb-signal);
}

.page-about .about-stage__head {
  display: flex;
  align-items: baseline;
  gap: 14px;
  flex-wrap: wrap;
}

.page-about .about-stage__no {
  font-family: var(--yb-font-mono);
  font-weight: 700;
  font-size: clamp(26px, 3.6vw, 40px);
  letter-spacing: 0.04em;
  line-height: 1;
  color: var(--yb-blue);
  opacity: 0.55;
}

.page-about .about-stage--key .about-stage__no {
  color: var(--yb-signal-deep);
  opacity: 1;
}

.page-about .about-stage__title {
  margin: 0;
  font-family: var(--yb-font-sans);
  font-weight: 700;
  font-size: clamp(18px, 2.4vw, 24px);
  line-height: 1.35;
  letter-spacing: 0.01em;
  color: var(--yb-ink);
}

.page-about .about-stage__body {
  margin: 12px 0 0;
  font-family: var(--yb-font-serif);
  font-size: 16px;
  line-height: 1.88;
  color: var(--yb-graphite);
  max-width: 42em;
}

.page-about .about-stage__more {
  margin-top: 14px;
  border-top: 1px dashed var(--yb-line);
  padding-top: 10px;
}

.page-about .about-stage__more summary {
  cursor: pointer;
  font-family: var(--yb-font-sans);
  font-size: 13px;
  font-weight: 700;
  letter-spacing: 0.06em;
  color: var(--yb-blue-deep);
  list-style: none;
  display: inline-flex;
  align-items: center;
  gap: 8px;
}

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

.page-about .about-stage__more summary::before {
  content: "+";
  font-family: var(--yb-font-mono);
  font-size: 15px;
  width: 16px;
  color: var(--yb-signal-deep);
}

.page-about .about-stage__more[open] summary::before {
  content: "–";
}

.page-about .about-stage__more p,
.page-about .about-stage__list {
  margin: 10px 0 0;
  font-family: var(--yb-font-serif);
  font-size: 15px;
  line-height: 1.85;
  color: var(--yb-graphite);
}

.page-about .about-stage__list {
  padding-left: 18px;
}

.page-about .about-stage__list li {
  margin-bottom: 6px;
}

.page-about .about-stage__list strong {
  font-family: var(--yb-font-sans);
  color: var(--yb-ink);
}

/* ---------- 现行用法 ---------- */
.page-about .about-now {
  padding: clamp(28px, 5vw, 72px) 0;
  background: var(--yb-blue-deep);
  color: #ffffff;
}

.page-about .about-now__grid {
  display: grid;
  gap: clamp(22px, 4vw, 52px);
  align-items: center;
}

.page-about .about-now .yb-eyebrow {
  color: var(--yb-signal);
}

.page-about .about-now__text .yb-h2 {
  margin-top: 12px;
  color: #ffffff;
  font-size: clamp(24px, 3.6vw, 38px);
  line-height: 1.2;
}

.page-about .about-now__text p {
  font-family: var(--yb-font-serif);
  font-size: 17px;
  line-height: 1.9;
  color: rgba(255, 255, 255, 0.84);
  max-width: 40em;
}

.page-about .about-now__link.yb-btn {
  margin-top: 8px;
  border-color: var(--yb-signal);
  color: #ffffff;
  background: transparent;
}

.page-about .about-now__link.yb-btn:hover {
  background: var(--yb-signal);
  color: var(--yb-ink);
}

.page-about .about-shot--now {
  border-color: rgba(255, 255, 255, 0.28);
  background: rgba(255, 255, 255, 0.08);
}

.page-about .about-shot--now .about-shot__caption {
  background: var(--yb-blue-deep);
  border-top-color: rgba(255, 255, 255, 0.22);
  color: rgba(255, 255, 255, 0.78);
}

/* ---------- 维护分工 ---------- */
.page-about .about-upkeep {
  padding: clamp(32px, 6vw, 92px) 0;
}

.page-about .about-upkeep__head {
  max-width: 44em;
}

.page-about .about-upkeep__head .yb-h2 {
  margin-top: 12px;
}

.page-about .about-upkeep__lede {
  margin: 14px 0 0;
  font-family: var(--yb-font-serif);
  font-size: 16px;
  line-height: 1.85;
  color: var(--yb-graphite);
}

.page-about .about-upkeep__grid {
  display: grid;
  gap: clamp(14px, 2vw, 20px);
  margin-top: clamp(22px, 3.4vw, 40px);
}

.page-about .about-role {
  padding: clamp(16px, 2.4vw, 26px);
  border: 1px solid var(--yb-line);
  border-top: 3px solid var(--yb-blue);
  background: #ffffff;
}

.page-about .about-role--structure {
  background: var(--yb-sand);
  border-top-color: var(--yb-signal);
}

.page-about .about-role__title {
  margin: 0;
  font-family: var(--yb-font-sans);
  font-weight: 700;
  font-size: 17px;
  letter-spacing: 0.02em;
  color: var(--yb-ink);
}

.page-about .about-role p {
  margin: 10px 0 0;
  font-family: var(--yb-font-serif);
  font-size: 15px;
  line-height: 1.85;
  color: var(--yb-graphite);
}

/* ---------- 收口 ---------- */
.page-about .about-next {
  padding: clamp(30px, 5vw, 72px) 0 clamp(48px, 8vw, 120px);
}

.page-about .about-next__inner {
  background: var(--yb-sand);
  border: 1px solid var(--yb-line);
  padding: clamp(22px, 4vw, 56px);
  display: grid;
  gap: clamp(20px, 3vw, 34px);
  align-items: end;
}

.page-about .about-next__text .yb-h2 {
  margin-top: 12px;
}

.page-about .about-next__text p {
  margin: 12px 0 0;
  max-width: 40em;
  font-family: var(--yb-font-serif);
  font-size: 16px;
  line-height: 1.85;
  color: var(--yb-graphite);
}

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

/* ---------- 响应式 ---------- */
@media (min-width: 720px) {
  .page-about .about-origin__grid {
    grid-template-columns: minmax(0, 6fr) minmax(0, 4fr);
  }

  .page-about .about-upkeep__grid {
    grid-template-columns: repeat(3, minmax(0, 1fr));
  }

  .page-about .about-role--structure {
    grid-column: span 1;
  }

  .page-about .about-next__inner {
    grid-template-columns: minmax(0, 7fr) minmax(0, 4fr);
  }
}

@media (min-width: 900px) {
  .page-about .about-hero__grid {
    grid-template-columns: minmax(0, 7fr) minmax(0, 4fr);
  }

  .page-about .about-track {
    grid-template-columns: var(--about-rail-w) minmax(0, 1fr);
    gap: clamp(26px, 4vw, 56px);
  }

  .page-about .about-rail {
    position: sticky;
    top: calc(var(--yb-header-h) + 26px);
  }

  .page-about .about-stage {
    width: calc(100% - var(--shrink, 0%));
  }

  .page-about .about-stage--s1 {
    --shrink: 20%;
  }

  .page-about .about-stage--s2 {
    --shrink: 13%;
  }

  .page-about .about-stage--s3 {
    --shrink: 7%;
  }

  .page-about .about-stage--s4 {
    --shrink: 3%;
  }

  .page-about .about-stage--s5 {
    --shrink: 0%;
  }

  .page-about .about-now__grid {
    grid-template-columns: minmax(0, 5fr) minmax(0, 4fr);
  }

  .page-about .about-upkeep__grid {
    grid-template-columns: minmax(0, 4fr) minmax(0, 3fr) minmax(0, 3fr);
  }
}

@media (min-width: 1180px) {
  .page-about .about-hero__facts {
    gap: 1px;
  }

  .page-about .about-stage__body {
    font-size: 17px;
  }
}

@media (prefers-reduced-motion: reduce) {
  .page-about .about-stage,
  .page-about .about-rail__link {
    transition: color 0.18s linear, border-color 0.18s linear, background-color 0.18s linear;
  }

  .page-about .about-stage:hover {
    transform: none;
  }
}