.page-start {
  --start-ruler-w: 22px;
  --start-toc-w: 236px;
  --start-sticky-top: 96px;
}

/* ---------- 首屏框景 ---------- */

.page-start .start-hero {
  padding-block-start: var(--space-3);
}

.page-start .start-hero__frame {
  position: relative;
  background-color: var(--color-surface-alt);
  box-shadow: var(--shadow-1);
  padding-block: calc(var(--space-6) + var(--space-2));
  padding-inline: var(--space-4);
}

.page-start .start-hero__frame::before,
.page-start .start-hero__frame::after {
  content: "";
  position: absolute;
  inset-inline: 0;
  height: 10px;
  background-image: repeating-linear-gradient(
    to right,
    var(--color-line) 0 var(--border-thin),
    transparent var(--border-thin) 14px
  );
  pointer-events: none;
}

.page-start .start-hero__frame::before { top: 0; }
.page-start .start-hero__frame::after { bottom: 0; }

.page-start .start-hero__grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: var(--space-6);
}

.page-start .start-hero__kicker {
  margin-block-end: var(--space-3);
}

.page-start .start-hero__title {
  font-family: var(--font-heading);
  font-size: var(--text-display);
  font-weight: var(--weight-heading);
  line-height: var(--leading-heading);
  letter-spacing: var(--tracking-heading);
  color: var(--color-ink);
  margin: 0;
  max-width: 14ch;
}

.page-start .start-hero__lede {
  font-size: var(--text-lg);
  line-height: var(--leading-body);
  color: var(--color-ink-soft);
  max-width: var(--measure);
  margin-block: var(--space-4) 0;
}

.page-start .start-hero__actions {
  list-style: none;
  margin: var(--space-4) 0 0;
  padding: 0;
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
}

.page-start .start-hero__visual {
  position: relative;
  padding-inline-end: calc(var(--start-ruler-w) + var(--space-2));
}

.page-start .start-stats {
  list-style: none;
  margin: 0 0 var(--space-4);
  padding: 0;
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: var(--space-2);
}

.page-start .start-stat {
  display: flex;
  flex-direction: column;
  gap: 2px;
  padding: var(--space-2);
  background-color: var(--color-surface);
  box-shadow: var(--shadow-1);
  border-inline-start: 3px solid var(--color-primary);
}

.page-start .start-stat--a { transform: translateY(0); }
.page-start .start-stat--b { transform: translateY(10px); border-inline-start-color: var(--color-accent); }
.page-start .start-stat--c { transform: translateY(4px); }
.page-start .start-stat--d { transform: translateY(14px); border-inline-start-color: var(--color-accent); }

.page-start .start-stat__num {
  font-family: var(--font-mono);
  font-size: var(--text-2xl);
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.1;
  color: var(--color-ink);
}

.page-start .start-stat__label {
  font-size: var(--text-sm);
  font-weight: 600;
  color: var(--color-primary);
}

.page-start .start-stat__note {
  font-size: var(--text-xs);
  line-height: 1.5;
  color: var(--color-ink-muted);
}

.page-start .start-hero__media {
  margin: var(--space-3) 0 0;
}

.page-start .start-hero__media img {
  display: block;
  width: 100%;
  height: auto;
  max-width: 100%;
  object-fit: cover;
  box-shadow: var(--shadow-2);
}

.page-start .start-ruler {
  position: absolute;
  inset-block: 0;
  inset-inline-end: 0;
  width: var(--start-ruler-w);
  height: 100%;
  color: var(--color-ink-muted);
}

/* ---------- 文档外壳 ---------- */

.page-start .start-shell {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: var(--space-6);
}

.page-start .start-toc__title {
  font-family: var(--font-heading);
  font-size: var(--text-lg);
  font-weight: 600;
  color: var(--color-ink);
  margin: 0 0 var(--space-3);
}

.page-start .start-toc__list {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  gap: var(--space-3);
}

.page-start .start-toc__link {
  display: block;
  font-size: var(--text-sm);
  font-weight: 600;
  color: var(--color-ink);
  text-decoration: none;
  padding-inline-start: var(--space-2);
  border-inline-start: 3px solid var(--color-primary);
  line-height: 1.5;
}

.page-start .start-toc__sections {
  list-style: none;
  margin: var(--space-1) 0 0;
  padding: 0;
  display: grid;
  gap: 4px;
}

.page-start .start-toc__sections a {
  display: block;
  font-size: var(--text-xs);
  font-family: var(--font-mono);
  color: var(--color-ink-muted);
  text-decoration: none;
  padding-inline-start: var(--space-2);
  line-height: 1.6;
}

.page-start .start-toc__sections a:hover,
.page-start .start-toc__sections a:focus-visible {
  color: var(--color-focus);
}

.page-start .start-article {
  max-width: var(--measure);
}

.page-start .start-chapter {
  margin-block-end: var(--section-y);
}

.page-start .start-chapter__no {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.14em;
  color: var(--color-primary);
  margin: 0 0 var(--space-1);
}

.page-start .start-chapter__title {
  font-family: var(--font-heading);
  font-size: var(--text-3xl);
  font-weight: var(--weight-heading);
  line-height: var(--leading-heading);
  color: var(--color-ink);
  margin: 0 0 var(--space-4);
}

.page-start .start-section {
  position: relative;
  scroll-margin-top: var(--start-sticky-top);
  padding-inline-start: var(--space-3);
  border-inline-start: 3px solid transparent;
  margin-block-end: var(--space-4);
  transition: border-color 0.24s ease, background-color 0.24s ease;
}

.page-start .start-section:target {
  border-inline-start-color: var(--color-primary);
  background-color: color-mix(in srgb, var(--color-highlight) 55%, transparent);
}

.page-start .start-section__title {
  font-family: var(--font-heading);
  font-size: var(--text-xl);
  font-weight: 600;
  line-height: var(--leading-heading);
  color: var(--color-ink);
  margin: 0 0 var(--space-2);
}

.page-start .start-section__text {
  font-size: var(--text-base);
  line-height: var(--leading-body);
  color: var(--color-ink-soft);
  margin: 0 0 var(--space-3);
}

.page-start .start-section__text a {
  color: var(--color-accent);
  text-decoration: underline;
  text-underline-offset: 3px;
}

.page-start .start-points {
  background-color: var(--color-highlight);
  padding: var(--space-2) var(--space-3);
  border-inline-start: 4px solid var(--color-primary);
}

.page-start .start-points__label {
  font-size: var(--text-xs);
  font-weight: 600;
  letter-spacing: 0.14em;
  color: var(--color-ink-muted);
  margin: 0 0 var(--space-1);
}

.page-start .start-points ul {
  margin: 0;
  padding-inline-start: 1.2em;
  display: grid;
  gap: 4px;
}

.page-start .start-points li {
  font-size: var(--text-sm);
  line-height: 1.7;
  color: var(--color-ink);
}

.page-start .start-points a {
  color: var(--color-accent);
  text-decoration: underline;
  text-underline-offset: 3px;
}

.page-start .start-takeaway {
  font-size: var(--text-sm);
  line-height: 1.7;
  color: var(--color-primary);
  margin: var(--space-2) 0 0;
  font-weight: 600;
}

/* ---------- 术语对照 ---------- */

.page-start .start-terms {
  margin-block-end: var(--section-y);
}

.page-start .start-terms__title {
  font-family: var(--font-heading);
  font-size: var(--text-3xl);
  font-weight: var(--weight-heading);
  color: var(--color-ink);
  margin: 0 0 var(--space-2);
}

.page-start .start-terms__intro {
  font-size: var(--text-base);
  line-height: var(--leading-body);
  color: var(--color-ink-soft);
  margin: 0 0 var(--space-4);
  max-width: var(--measure);
}

.page-start .start-terms__list {
  margin: 0;
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: var(--space-3);
}

.page-start .start-term {
  padding-inline-start: var(--space-3);
  border-inline-start: 3px solid var(--color-primary-soft);
}

.page-start .start-term__key {
  font-family: var(--font-mono);
  font-size: var(--text-base);
  font-weight: 700;
  letter-spacing: -0.01em;
  color: var(--color-ink);
  margin: 0 0 4px;
}

.page-start .start-term__desc {
  margin: 0;
  font-size: var(--text-sm);
  line-height: 1.7;
  color: var(--color-ink-soft);
}

/* ---------- 三条路径 ---------- */

.page-start .start-paths {
  margin-block-end: var(--section-y);
}

.page-start .start-paths__title {
  font-family: var(--font-heading);
  font-size: var(--text-3xl);
  font-weight: var(--weight-heading);
  color: var(--color-ink);
  margin: 0 0 var(--space-4);
}

.page-start .start-paths__grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: var(--space-4);
}

.page-start .start-paths__media {
  order: 2;
}

.page-start .start-paths__media figure {
  margin: 0;
}

.page-start .start-paths__media img {
  display: block;
  width: 100%;
  height: auto;
  max-width: 100%;
  object-fit: cover;
  box-shadow: var(--shadow-2);
}

.page-start .path-board {
  order: 1;
  background-color: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
  padding: var(--space-4) var(--space-3);
}

.page-start .path-board__label {
  font-size: var(--text-xs);
  letter-spacing: 0.16em;
  font-weight: 600;
  color: var(--color-contrast-accent);
  margin: 0 0 var(--space-3);
}

.page-start .path-board__steps {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  gap: var(--space-4);
}

.page-start .path-board__step {
  padding-block-start: var(--space-3);
  border-block-start: var(--border-thin) solid var(--color-contrast-line);
}

.page-start .path-board__step:first-child {
  padding-block-start: 0;
  border-block-start: 0;
}

.page-start .path-board__head {
  display: flex;
  align-items: baseline;
  gap: var(--space-2);
  margin: 0 0 var(--space-1);
}

.page-start .path-board__num {
  font-family: var(--font-mono);
  font-size: var(--text-lg);
  font-weight: 700;
  letter-spacing: -0.02em;
  color: var(--color-contrast-accent);
}

.page-start .path-board__name {
  font-family: var(--font-heading);
  font-size: var(--text-lg);
  font-weight: 600;
  color: var(--color-contrast-ink);
}

.page-start .path-board__body {
  margin: 0 0 var(--space-2);
  font-size: var(--text-sm);
  line-height: 1.75;
  color: var(--color-contrast-ink);
}

.page-start .path-board__link {
  margin: 0;
}

.page-start .path-board__link a {
  font-size: var(--text-xs);
  font-weight: 600;
  letter-spacing: 0.08em;
  color: var(--color-contrast-accent);
  text-decoration: none;
  border-block-end: var(--border-thin) solid var(--color-contrast-accent);
  padding-block-end: 2px;
}

.page-start .path-board__link a:hover,
.page-start .path-board__link a:focus-visible {
  color: var(--color-contrast-ink);
  border-block-end-color: var(--color-contrast-ink);
}

/* ---------- 下一步入口 ---------- */

.page-start .start-next__title {
  font-family: var(--font-heading);
  font-size: var(--text-3xl);
  font-weight: var(--weight-heading);
  color: var(--color-ink);
  margin: 0 0 var(--space-2);
}

.page-start .start-next__lede {
  font-size: var(--text-base);
  line-height: var(--leading-body);
  color: var(--color-ink-soft);
  margin: 0 0 var(--space-4);
  max-width: var(--measure);
}

.page-start .start-next__media {
  margin: 0 0 var(--space-4);
}

.page-start .start-next__media img {
  display: block;
  width: 100%;
  height: auto;
  max-width: 100%;
  object-fit: cover;
  box-shadow: var(--shadow-2);
}

.page-start .start-next__links {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: var(--space-2);
}

.page-start .next-link a {
  display: block;
  padding: var(--space-2) var(--space-3);
  background-color: var(--color-surface-alt);
  box-shadow: var(--shadow-1);
  text-decoration: none;
  border-inline-start: 3px solid var(--color-primary);
}

.page-start .next-link a:hover,
.page-start .next-link a:focus-visible {
  background-color: var(--color-primary-soft);
  border-inline-start-color: var(--color-accent);
}

.page-start .next-link__title {
  display: block;
  font-family: var(--font-heading);
  font-size: var(--text-lg);
  font-weight: 600;
  color: var(--color-ink);
  margin-block-end: 2px;
}

.page-start .next-link__desc {
  display: block;
  font-size: var(--text-sm);
  line-height: 1.7;
  color: var(--color-ink-soft);
}

.page-start .next-link__arrow {
  display: block;
  margin-block-start: var(--space-1);
  font-size: var(--text-xs);
  font-weight: 600;
  letter-spacing: 0.12em;
  color: var(--color-accent);
}

/* ---------- 键盘焦点 ---------- */

.page-start a:focus-visible {
  outline: 2px solid var(--color-focus);
  outline-offset: 2px;
}

/* ---------- 中等屏幕 ---------- */

@media (min-width: 768px) {
  .page-start .start-hero__frame {
    padding-inline: var(--space-6);
  }

  .page-start .start-stats {
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: var(--space-3);
  }

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

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

  .page-start .start-paths__grid {
    grid-template-columns: minmax(0, 0.72fr) minmax(0, 1.28fr);
    gap: var(--space-6);
  }

  .page-start .start-paths__media,
  .page-start .path-board {
    order: 0;
  }
}

/* ---------- 桌面 ---------- */

@media (min-width: 1024px) {
  .page-start .start-hero__grid {
    grid-template-columns: minmax(0, 1.05fr) minmax(0, 0.95fr);
    gap: var(--space-8);
    align-items: start;
  }

  .page-start .start-hero__frame {
    padding-block: calc(var(--space-8) + var(--space-2));
    padding-inline: var(--space-8);
  }

  .page-start .start-hero__visual {
    padding-inline-end: calc(var(--start-ruler-w) + var(--space-3));
  }

  .page-start .start-shell {
    grid-template-columns: var(--start-toc-w) minmax(0, 1fr);
    gap: var(--space-8);
    align-items: start;
  }

  .page-start .start-toc {
    position: sticky;
    top: var(--start-sticky-top);
    align-self: start;
    padding-block-start: var(--space-1);
  }

  .page-start .start-article {
    max-width: none;
  }

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

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

  .page-start .start-chapter__title,
  .page-start .start-terms__title,
  .page-start .start-paths__title,
  .page-start .start-next__title {
    font-size: var(--text-4xl);
  }
}

/* ---------- 动效协议 ---------- */

.page-start [data-reveal] {
  opacity: 0;
  transform: translateY(10px);
  transition: opacity 0.45s ease, transform 0.45s ease;
}

.page-start [data-reveal].is-visible {
  opacity: 1;
  transform: translateY(0);
}

.page-start .start-stat--b.is-visible { transform: translateY(10px); }
.page-start .start-stat--c.is-visible { transform: translateY(4px); }
.page-start .start-stat--d.is-visible { transform: translateY(14px); }

@media (prefers-reduced-motion: reduce) {
  .page-start [data-reveal] {
    opacity: 1;
    transform: none;
    transition: none;
  }

  .page-start .start-stat--b,
  .page-start .start-stat--c,
  .page-start .start-stat--d {
    transform: none;
  }

  .page-start .start-section {
    transition: none;
  }
}