:root {
  --color-paper: #f7f2ea;
  --color-amber: #c48a2c;
  --color-ink: #1e3a32;
  --color-about-bg: #e4ebe7;
  --color-ink-muted: rgba(30, 58, 50, 0.72);
  --color-border: rgba(30, 58, 50, 0.18);
  --font-sans: "PingFang SC", "Hiragino Sans GB", "Noto Sans SC", "Microsoft YaHei", sans-serif;
  --font-serif: "Songti SC", "Noto Serif SC", "STSong", "SimSun", serif;
  --space-xs: 0.5rem;
  --space-sm: 0.75rem;
  --space-md: 1.25rem;
  --space-lg: 2rem;
  --space-xl: 3rem;
  --max-content: 72rem;
  --chapter-width: 18%;
  --main-width: 82%;
  --top-bar-h: 3rem;
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
  overflow-x: hidden;
}

body {
  margin: 0;
  font-family: var(--font-sans);
  font-size: 1rem;
  line-height: 1.65;
  color: var(--color-ink);
  background: var(--color-paper);
  overflow-x: hidden;
}

img,
svg {
  max-width: 100%;
  height: auto;
  display: block;
}

a {
  color: var(--color-ink);
}

a:focus-visible,
button:focus-visible {
  outline: 2px solid var(--color-amber);
  outline-offset: 2px;
}

.site-shell {
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

.chapter-nav {
  display: none;
}

.main-column {
  flex: 1;
  width: 100%;
  min-width: 0;
}

.top-bar {
  position: sticky;
  top: 0;
  z-index: 20;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-sm);
  min-height: var(--top-bar-h);
  padding: var(--space-xs) var(--space-md);
  background: var(--color-paper);
  border-bottom: 1px solid var(--color-border);
}

.top-bar__logo {
  font-family: var(--font-serif);
  font-size: 1.125rem;
  font-weight: 600;
  text-decoration: none;
  letter-spacing: 0.04em;
}

.top-bar__toggle {
  font: inherit;
  padding: 0.35rem 0.65rem;
  border: 1px solid var(--color-ink);
  background: transparent;
  color: var(--color-ink);
  cursor: pointer;
}

.top-bar__nav {
  display: none;
  position: absolute;
  top: 100%;
  left: 0;
  right: 0;
  flex-direction: column;
  background: var(--color-paper);
  border-bottom: 1px solid var(--color-border);
  padding: var(--space-sm) var(--space-md) var(--space-md);
}

.top-bar__nav.is-open {
  display: flex;
}

.top-bar__nav a {
  padding: 0.65rem 0;
  text-decoration: none;
  border-bottom: 1px solid var(--color-border);
}

.top-bar__nav a:last-child {
  border-bottom: none;
}

.content-flow {
  padding: 0 var(--space-md) var(--space-xl);
}

.section-label {
  font-family: var(--font-serif);
  font-size: 0.875rem;
  font-weight: 600;
  letter-spacing: 0.12em;
  color: var(--color-ink-muted);
  margin: 0 0 var(--space-md);
}

.hero {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--space-lg);
  padding: var(--space-lg) 0 var(--space-xl);
  align-items: start;
}

.hero__claim {
  font-family: var(--font-serif);
  font-size: clamp(1.5rem, 5vw, 2.25rem);
  line-height: 1.35;
  margin: 0 0 var(--space-md);
  font-weight: 600;
}

.hero__subtitle {
  margin: 0 0 var(--space-lg);
  color: var(--color-ink-muted);
  max-width: 36em;
}

.hero__actions {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-sm);
}

.btn {
  display: inline-block;
  padding: 0.55rem 1.1rem;
  text-decoration: none;
  font-size: 0.9375rem;
  border: 1px solid var(--color-ink);
  transition: background 0.2s ease, color 0.2s ease;
}

.btn--primary {
  background: var(--color-ink);
  color: var(--color-paper);
}

.btn--ghost {
  background: transparent;
  color: var(--color-ink);
}

.btn--primary:hover,
.btn--primary:focus-visible {
  background: var(--color-amber);
  border-color: var(--color-amber);
  color: var(--color-paper);
}

.btn--ghost:hover,
.btn--ghost:focus-visible {
  border-color: var(--color-amber);
  color: var(--color-amber);
}

.hero__aside {
  position: relative;
  display: flex;
  flex-direction: row;
  align-items: flex-start;
  justify-content: flex-end;
  gap: var(--space-sm);
  min-width: 0;
}

.hero__strip {
  writing-mode: vertical-rl;
  text-orientation: mixed;
  margin: 0;
  padding: var(--space-sm) var(--space-xs);
  font-family: var(--font-serif);
  font-size: 0.9375rem;
  letter-spacing: 0.08em;
  background: var(--color-amber);
  color: var(--color-paper);
  border-radius: 2px;
  transform: translateY(var(--strip-offset, 0));
  transition: transform 0.15s ease-out;
  max-height: 16rem;
}

.hero__diagram {
  flex: 1 1 auto;
  max-width: min(100%, 280px);
}

.about {
  margin: 0 calc(-1 * var(--space-md)) var(--space-xl);
  padding: var(--space-xl) var(--space-md);
  background: var(--color-about-bg);
}

.about__body {
  max-width: 40rem;
}

.about__body p {
  margin: 0 0 var(--space-md);
}

.about__body p:last-child {
  margin-bottom: 0;
}

.about__highlight {
  border-left: 4px solid var(--color-amber);
  padding-left: var(--space-md);
}

.services {
  position: relative;
  margin-bottom: var(--space-xl);
}

.services__connector {
  display: none;
  position: absolute;
  left: 0.5rem;
  top: 3rem;
  width: 2rem;
  height: calc(100% - 4rem);
  color: var(--color-amber);
  opacity: 0;
  pointer-events: none;
}

.services.is-active .services__connector {
  opacity: var(--connector-opacity, 0.35);
}

.services.is-active #services-path {
  stroke-dasharray: var(--path-length, 600);
  stroke-dashoffset: var(--path-offset, 600);
  transition: stroke-dashoffset 0.4s ease-out;
}

.services__ladder {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-direction: column;
  gap: var(--space-md);
}

.service-card {
  border: 1px solid var(--color-border);
  background: rgba(247, 242, 234, 0.6);
  padding: var(--space-md);
}

.service-card h3 {
  font-family: var(--font-serif);
  font-size: 1.125rem;
  margin: 0 0 var(--space-xs);
}

.service-card__hook {
  margin: 0 0 var(--space-sm);
  font-size: 0.9375rem;
  color: var(--color-amber);
  font-weight: 600;
}

.service-card__body {
  margin: 0;
  font-size: 0.9375rem;
  color: var(--color-ink-muted);
}

.service-card--wide {
  display: flex;
  flex-direction: column;
  gap: var(--space-md);
}

.service-card__visual {
  align-self: center;
}

.service-card--bar {
  padding: var(--space-sm) var(--space-md);
}

.service-card--bar h3 {
  display: inline;
  margin-right: var(--space-sm);
}

.service-card--bar .service-card__hook {
  display: inline;
  margin: 0 var(--space-sm) 0 0;
}

.service-card--bar .service-card__body {
  margin-top: var(--space-xs);
}

.advantages {
  margin-bottom: var(--space-xl);
}

.advantages__grid {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--space-md);
}

.advantage-item {
  border-left: 4px solid var(--color-amber);
  padding: var(--space-md) var(--space-md) var(--space-md) var(--space-sm);
  background: rgba(30, 58, 50, 0.04);
}

.advantage-item h3 {
  font-family: var(--font-serif);
  font-size: 1.0625rem;
  margin: 0 0 var(--space-xs);
}

.advantage-item p {
  margin: 0;
  font-size: 0.9375rem;
  color: var(--color-ink-muted);
}

.site-footer {
  border-top: 3px double var(--color-border);
  padding: var(--space-lg) var(--space-md) var(--space-xl);
  text-align: center;
  font-size: 0.875rem;
}

.site-footer__copy {
  margin: 0 0 var(--space-sm);
}

.site-footer__beian {
  margin: 0;
}

.site-footer__beian a {
  color: var(--color-ink-muted);
  text-decoration: none;
}

.site-footer__beian a:hover,
.site-footer__beian a:focus-visible {
  color: var(--color-amber);
}

@media (orientation: landscape) and (max-height: 500px) {
  .hero {
    padding-top: var(--space-sm);
    padding-bottom: var(--space-md);
    gap: var(--space-md);
  }

  .hero__claim {
    font-size: 1.35rem;
    margin-bottom: var(--space-sm);
  }

  .hero__subtitle {
    margin-bottom: var(--space-md);
    font-size: 0.875rem;
  }

  .hero__diagram {
    max-height: 140px;
    width: auto;
  }

  .hero__strip {
    max-height: 10rem;
    font-size: 0.8125rem;
  }

  .top-bar {
    position: relative;
  }
}

@media (min-width: 768px) {
  .top-bar__toggle {
    display: none;
  }

  .top-bar {
    position: relative;
    justify-content: space-between;
    padding: var(--space-sm) var(--space-lg);
  }

  .top-bar__nav {
    display: flex;
    position: static;
    flex-direction: row;
    gap: var(--space-lg);
    border: none;
    padding: 0;
    background: transparent;
  }

  .top-bar__nav a {
    padding: 0.25rem 0;
    border: none;
    text-decoration: none;
    font-size: 0.9375rem;
  }

  .top-bar__nav a:hover,
  .top-bar__nav a:focus-visible {
    color: var(--color-amber);
  }

  .content-flow {
    padding-left: var(--space-lg);
    padding-right: var(--space-lg);
  }

  .hero {
    grid-template-columns: 1.1fr 0.9fr;
    gap: var(--space-md);
  }

  .service-card--wide {
    flex-direction: row;
    align-items: center;
  }

  .service-card__text {
    flex: 1 1 55%;
    min-width: 0;
  }

  .service-card__visual {
    flex: 0 1 45%;
  }

  .services__ladder {
    display: grid;
    grid-template-columns: 1fr 1fr;
    grid-template-areas:
      "wide wide"
      "half-a half-b"
      "bar bar";
    gap: var(--space-md);
  }

  .service-card--wide {
    grid-area: wide;
  }

  .services__ladder li:nth-child(2) {
    grid-area: half-a;
  }

  .services__ladder li:nth-child(3) {
    grid-area: half-b;
  }

  .service-card--bar {
    grid-area: bar;
  }

  .advantages__grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (min-width: 1100px) {
  .site-shell {
    flex-direction: row;
    align-items: stretch;
  }

  .chapter-nav {
    display: flex;
    flex-direction: column;
    flex: 0 0 var(--chapter-width);
    max-width: var(--chapter-width);
    position: sticky;
    top: 0;
    align-self: flex-start;
    min-height: 100vh;
    padding: var(--space-xl) var(--space-md) var(--space-lg);
    border-right: 1px solid var(--color-border);
    background: var(--color-paper);
  }

  .chapter-nav__brand {
    font-family: var(--font-serif);
    font-size: 1.25rem;
    margin: 0 0 var(--space-xl);
    letter-spacing: 0.06em;
  }

  .chapter-nav__links {
    display: flex;
    flex-direction: column;
    gap: var(--space-md);
  }

  .chapter-nav__links a {
    text-decoration: none;
    font-size: 0.9375rem;
    padding: 0.15rem 0;
    border-left: 2px solid transparent;
    padding-left: var(--space-sm);
  }

  .chapter-nav__links a:hover,
  .chapter-nav__links a:focus-visible {
    border-left-color: var(--color-amber);
    color: var(--color-amber);
  }

  .main-column {
    flex: 1 1 var(--main-width);
    max-width: var(--main-width);
    min-width: 0;
  }

  .top-bar__nav {
    display: none;
  }

  .top-bar__toggle {
    display: none;
  }

  .top-bar {
    padding-left: var(--space-xl);
    padding-right: var(--space-xl);
  }

  .content-flow {
    padding: 0 var(--space-xl) var(--space-xl);
  }

  .about {
    margin-left: calc(-1 * var(--space-xl));
    margin-right: calc(-1 * var(--space-xl));
    padding-left: var(--space-xl);
    padding-right: var(--space-xl);
  }

  .services__connector {
    display: block;
  }

  .services__ladder {
    padding-left: var(--space-lg);
  }

  .advantages__grid {
    grid-template-columns: repeat(3, 1fr);
    align-items: start;
  }

  .advantage-item--sink {
    margin-top: var(--space-lg);
  }

  .advantages__grid .advantage-item:nth-child(1) {
    grid-column: 1;
    grid-row: 1;
  }

  .advantages__grid .advantage-item:nth-child(2) {
    grid-column: 2;
    grid-row: 1;
  }

  .advantages__grid .advantage-item:nth-child(3) {
    grid-column: 3;
    grid-row: 1;
  }

  .advantages__grid .advantage-item:nth-child(4) {
    grid-column: 2;
    grid-row: 2;
    margin-top: 0;
  }
}

@media (min-width: 1440px) {
  .main-column {
    max-width: calc(var(--max-content) * 0.82);
  }

  .site-shell {
    justify-content: center;
    padding: 0 max(0px, calc((100vw - var(--max-content)) / 2));
  }

  .chapter-nav {
    flex-basis: calc(var(--max-content) * 0.18);
    max-width: calc(var(--max-content) * 0.18);
  }

  .hero__claim {
    font-size: 2.35rem;
  }
}

@media (min-aspect-ratio: 2/1) {
  .content-flow {
    max-width: 56rem;
    margin: 0 auto;
  }

  .hero {
    grid-template-columns: 1.2fr 0.8fr;
  }

  .about__body {
    max-width: 48rem;
    column-count: 1;
  }
}

@media (max-aspect-ratio: 3/4) {
  .hero__aside {
    flex-direction: column;
    align-items: stretch;
  }

  .hero__strip {
    writing-mode: horizontal-tb;
    text-orientation: mixed;
    max-height: none;
    align-self: flex-start;
  }

  .hero__diagram {
    max-width: 100%;
  }

  .section-label {
    font-size: 0.8125rem;
  }
}