.page-about {
  --about-index-w: 176px;
  --about-gap: clamp(44px, 7vw, 88px);
  padding-block: clamp(20px, 4vw, 40px) clamp(56px, 8vw, 104px);
}

/* ---------- 首屏 ---------- */
.page-about .about-hero {
  position: relative;
  margin-top: 20px;
  padding: clamp(26px, 5vw, 52px) clamp(20px, 4.5vw, 52px);
  border: 1px solid var(--line);
  border-radius: var(--r-lg);
  overflow: hidden;
  background:
    radial-gradient(115% 95% at 92% -10%, rgba(47, 243, 208, 0.16), transparent 60%),
    radial-gradient(80% 70% at 0% 110%, rgba(255, 106, 43, 0.10), transparent 62%),
    linear-gradient(158deg, var(--panel), var(--arena) 78%);
}

.page-about .about-hero::after {
  content: "";
  position: absolute;
  inset: 0;
  pointer-events: none;
  background:
    repeating-linear-gradient(90deg, rgba(28, 69, 105, 0.55) 0 1px, transparent 1px 64px),
    repeating-linear-gradient(0deg, rgba(28, 69, 105, 0.4) 0 1px, transparent 1px 64px);
  -webkit-mask-image: radial-gradient(120% 90% at 80% 10%, #000 8%, transparent 72%);
  mask-image: radial-gradient(120% 90% at 80% 10%, #000 8%, transparent 72%);
  opacity: 0.7;
}

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

.page-about .about-hero__title {
  margin: 10px 0 0;
  font-family: var(--font-display);
  font-weight: 900;
  font-size: clamp(28px, 6.4vw, 58px);
  line-height: 1.1;
  letter-spacing: -0.02em;
  color: var(--white);
  max-width: 18ch;
}

.page-about .about-hero__lead {
  margin: 18px 0 0;
  max-width: 46ch;
  font-size: 16px;
  line-height: 1.78;
  color: var(--text);
}

.page-about .about-hero__facts {
  list-style: none;
  margin: 28px 0 0;
  padding: 0;
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 1px;
  background: var(--line);
  border-radius: var(--r-md);
  overflow: hidden;
}

.page-about .about-fact {
  display: flex;
  flex-direction: column;
  gap: 4px;
  padding: 14px 16px;
  background: var(--arena);
}

.page-about .about-fact__num {
  font-family: var(--font-mono);
  font-size: clamp(22px, 3.4vw, 30px);
  font-weight: 700;
  line-height: 1.1;
  letter-spacing: -0.01em;
  color: var(--white);
}

.page-about .about-fact__unit {
  margin-left: 3px;
  font-family: var(--font-body);
  font-size: 12px;
  font-weight: 500;
  letter-spacing: 0;
  color: var(--cyan);
}

.page-about .about-fact__label {
  font-size: 12.5px;
  line-height: 1.4;
  color: var(--graphite);
}

/* ---------- 主体两栏 ---------- */
.page-about .about-body {
  margin-top: clamp(38px, 6vw, 76px);
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: clamp(24px, 4vw, 40px);
}

/* ---------- 章节索引 ---------- */
.page-about .about-index__title {
  margin: 0;
  font-family: var(--font-mono);
  font-size: 11.5px;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--graphite);
}

.page-about .about-index__list {
  list-style: none;
  margin: 10px 0 0;
  padding: 0 0 4px;
  display: flex;
  gap: 8px;
  overflow-x: auto;
  scrollbar-width: thin;
}

.page-about .about-index__link {
  display: inline-flex;
  align-items: baseline;
  gap: 7px;
  padding: 7px 14px;
  border: 1px solid var(--line);
  border-radius: var(--r-pill);
  color: var(--graphite);
  font-size: 13.5px;
  line-height: 1.4;
  white-space: nowrap;
  text-decoration: none;
  transition: color 0.16s var(--ease), border-color 0.16s var(--ease), background-color 0.16s var(--ease);
}

.page-about .about-index__num {
  font-family: var(--font-mono);
  font-size: 11.5px;
  letter-spacing: 0.06em;
  color: var(--cyan);
}

.page-about .about-index__link:hover,
.page-about .about-index__link:focus-visible {
  color: var(--white);
  border-color: var(--cyan);
  background: rgba(47, 243, 208, 0.09);
}

/* ---------- 研究板章节 ---------- */
.page-about .board {
  scroll-margin-top: calc(var(--header-h, 60px) + 24px);
}

.page-about .board + .board {
  margin-top: var(--about-gap);
}

.page-about .board__head {
  padding-left: 16px;
  border-left: 4px solid var(--cyan);
}

.page-about .board__coord {
  margin: 0;
  font-family: var(--font-mono);
  font-size: 11.5px;
  letter-spacing: 0.16em;
  color: var(--cyan);
}

.page-about .board__title {
  margin: 8px 0 0;
  font-family: var(--font-display);
  font-weight: 900;
  font-size: clamp(21px, 3.8vw, 34px);
  line-height: 1.24;
  letter-spacing: -0.02em;
  color: var(--white);
}

.page-about .board__body {
  margin-top: 22px;
  padding-left: 20px;
  border-left: 1px solid var(--line);
}

.page-about .board__body > p {
  margin: 0;
  max-width: 48ch;
  font-size: 16px;
  line-height: 1.78;
  color: var(--text);
}

.page-about .board__body > p + p {
  margin-top: 16px;
}

/* ---------- 图注 ---------- */
.page-about .board__figure {
  margin: 26px 0 0;
}

.page-about .board__figure img {
  display: block;
  width: 100%;
  max-width: 100%;
  height: auto;
  object-fit: cover;
  border: 1px solid var(--line);
  border-radius: var(--r-md);
  background: var(--panel);
}

.page-about .board__figure figcaption {
  margin-top: 10px;
  font-size: 13px;
  line-height: 1.65;
  color: var(--graphite);
}

/* ---------- 里程碑折叠 ---------- */
.page-about .milestones {
  position: relative;
  margin-top: 28px;
  padding-left: 18px;
}

.page-about .milestones::before {
  content: "";
  position: absolute;
  left: 0;
  top: 10px;
  bottom: 10px;
  width: 1px;
  background: linear-gradient(180deg, var(--cyan), var(--line) 58%, transparent);
}

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

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

.page-about .milestone__summary {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: 4px 14px;
  padding: 15px 0;
  cursor: pointer;
  list-style: none;
}

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

.page-about .milestone__mark {
  grid-column: 1;
  font-family: var(--font-mono);
  font-size: 12.5px;
  letter-spacing: 0.08em;
  color: var(--cyan);
}

.page-about .milestone__title {
  grid-column: 1;
  font-size: 16.5px;
  font-weight: 700;
  line-height: 1.5;
  color: var(--white);
}

.page-about .milestone__sign {
  grid-column: 2;
  grid-row: 1 / span 2;
  align-self: center;
  font-family: var(--font-mono);
  font-size: 20px;
  line-height: 1;
  color: var(--graphite);
  transition: transform 0.2s var(--ease), color 0.2s var(--ease);
}

.page-about .milestone[open] .milestone__sign {
  transform: rotate(45deg);
  color: var(--cyan);
}

.page-about .milestone__body {
  padding: 0 0 18px;
}

.page-about .milestone__body p {
  margin: 0;
  max-width: 46ch;
  font-size: 15px;
  line-height: 1.75;
  color: var(--text);
}

/* ---------- 证据小卡 ---------- */
.page-about .evidence {
  list-style: none;
  margin: 26px 0 0;
  padding: 0;
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(132px, 1fr));
  gap: 1px;
  background: var(--line);
  border: 1px solid var(--line);
  border-radius: var(--r-md);
  overflow: hidden;
}

.page-about .evidence__item {
  padding: 15px 16px;
  background: var(--panel);
}

.page-about .evidence__num {
  display: block;
  font-family: var(--font-mono);
  font-size: clamp(22px, 2.8vw, 28px);
  font-weight: 700;
  line-height: 1.15;
  letter-spacing: -0.01em;
  color: var(--cyan);
}

.page-about .evidence__label {
  display: block;
  margin-top: 6px;
  font-size: 12.5px;
  line-height: 1.5;
  color: var(--graphite);
}

/* ---------- 三段时间 ---------- */
.page-about .phase {
  list-style: none;
  margin: 28px 0 0;
  padding: 0;
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: 12px;
}

.page-about .phase__item {
  position: relative;
  padding: 18px 18px 18px 22px;
  border: 1px solid var(--line);
  border-radius: var(--r-md);
  background: linear-gradient(150deg, rgba(13, 42, 71, 0.9), rgba(6, 26, 46, 0.9));
}

.page-about .phase__item::before {
  content: "";
  position: absolute;
  left: 0;
  top: 18px;
  bottom: 18px;
  width: 3px;
  border-radius: var(--r-pill);
  background: linear-gradient(180deg, var(--cyan), rgba(47, 243, 208, 0.15));
}

.page-about .phase__time {
  display: block;
  font-family: var(--font-mono);
  font-size: 12.5px;
  letter-spacing: 0.06em;
  color: var(--orange);
}

.page-about .phase__title {
  margin: 8px 0 0;
  font-size: 17px;
  font-weight: 800;
  line-height: 1.4;
  letter-spacing: -0.01em;
  color: var(--white);
}

.page-about .phase__item p {
  margin: 8px 0 0;
  font-size: 15px;
  line-height: 1.75;
  color: var(--text);
}

/* ---------- 术语卡 ---------- */
.page-about .term {
  position: relative;
  display: inline-block;
  color: var(--mist);
  border-bottom: 1px dashed rgba(47, 243, 208, 0.55);
  cursor: help;
}

.page-about .term__pop {
  position: absolute;
  left: 0;
  bottom: calc(100% + 10px);
  z-index: 6;
  width: min(238px, 68vw);
  padding: 10px 12px;
  border: 1px solid var(--cyan);
  border-radius: var(--r-sm);
  background: var(--panel);
  color: var(--text);
  font-size: 13px;
  line-height: 1.62;
  text-align: left;
  opacity: 0;
  visibility: hidden;
  transform: translateY(6px);
  transition: opacity 0.16s var(--ease), transform 0.16s var(--ease), visibility 0.16s;
}

.page-about .term:hover .term__pop,
.page-about .term:focus .term__pop,
.page-about .term:focus-visible .term__pop {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

/* ---------- 下一步 ---------- */
.page-about .about-next {
  margin-top: var(--about-gap);
  padding: clamp(22px, 4vw, 40px) clamp(20px, 4vw, 40px);
  border: 1px solid var(--line);
  border-radius: var(--r-lg);
  background:
    radial-gradient(90% 120% at 100% 0%, rgba(47, 243, 208, 0.10), transparent 58%),
    var(--panel);
}

.page-about .about-next__title {
  margin: 0;
  font-family: var(--font-display);
  font-weight: 900;
  font-size: clamp(20px, 3.2vw, 28px);
  line-height: 1.28;
  letter-spacing: -0.02em;
  color: var(--white);
}

.page-about .about-next__lead {
  margin: 12px 0 0;
  max-width: 44ch;
  font-size: 15.5px;
  line-height: 1.75;
  color: var(--text);
}

.page-about .about-next__list {
  list-style: none;
  margin: 24px 0 0;
  padding: 0;
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: 1px;
  background: var(--line);
  border: 1px solid var(--line);
  border-radius: var(--r-md);
  overflow: hidden;
}

.page-about .about-next__item {
  display: flex;
  flex-direction: column;
  gap: 6px;
  padding: 15px 16px;
  background: var(--arena);
}

.page-about .about-next__link {
  font-size: 15.5px;
  font-weight: 700;
  color: var(--cyan);
  text-decoration: none;
  transition: color 0.16s var(--ease);
}

.page-about .about-next__link::after {
  content: " →";
  font-family: var(--font-mono);
  font-size: 13px;
}

.page-about .about-next__link:hover,
.page-about .about-next__link:focus-visible {
  color: var(--white);
}

.page-about .about-next__note {
  font-size: 13.5px;
  line-height: 1.65;
  color: var(--graphite);
}

.page-about .about-next__cta {
  margin-top: 24px;
}

/* ---------- 断点 ---------- */
@media (min-width: 640px) {
  .page-about .about-hero__facts {
    grid-template-columns: repeat(4, minmax(0, 1fr));
  }

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

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

@media (min-width: 1024px) {
  .page-about .about-body {
    grid-template-columns: var(--about-index-w) minmax(0, 1fr);
    gap: clamp(32px, 4.5vw, 60px);
    align-items: start;
  }

  .page-about .about-index {
    position: sticky;
    top: calc(var(--header-h, 60px) + 28px);
    padding-right: 4px;
    border-right: 1px solid var(--line);
  }

  .page-about .about-index__list {
    flex-direction: column;
    gap: 4px;
    overflow: visible;
    padding-bottom: 0;
  }

  .page-about .about-index__link {
    display: flex;
    border-color: transparent;
    border-radius: var(--r-sm);
    padding: 8px 12px;
  }

  .page-about .board__body {
    padding-left: 26px;
  }
}

@media (min-width: 1280px) {
  .page-about .about-hero {
    padding-inline: 56px;
  }

  .page-about .board__body > p,
  .page-about .milestone__body p {
    font-size: 16.5px;
  }
}

@media (prefers-reduced-motion: reduce) {
  .page-about .about-index__link,
  .page-about .milestone__sign,
  .page-about .term__pop,
  .page-about .about-next__link {
    transition: none;
  }

  .page-about .term__pop {
    transform: none;
  }
}