:root {
  --ink: #17171c;
  --paper: #ffffff;
  --soft: #f2f4f5;
  --muted: #666871;
  --coral: #ff5a4f;
  --coral-dark: #dd3f36;
  --mint: #51c8b7;
  --yellow: #ffd04a;
  --line: #17171c;
  --shadow: 6px 6px 0 #17171c;
  --max-width: 1180px;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  color: var(--ink);
  background: var(--paper);
  font-family: "Microsoft YaHei", "PingFang SC", Arial, sans-serif;
  font-size: 16px;
  line-height: 1.75;
  letter-spacing: 0;
}

body.menu-open {
  overflow: hidden;
}

img {
  display: block;
  max-width: 100%;
}

a {
  color: inherit;
  text-decoration: none;
}

button,
a {
  -webkit-tap-highlight-color: transparent;
}

:focus-visible {
  outline: 3px solid var(--mint);
  outline-offset: 3px;
}

.skip-link {
  position: fixed;
  top: 10px;
  left: 10px;
  z-index: 100;
  padding: 8px 14px;
  color: var(--paper);
  background: var(--ink);
  transform: translateY(-150%);
}

.skip-link:focus {
  transform: translateY(0);
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  border-bottom: 2px solid var(--line);
  background: rgba(255, 255, 255, 0.96);
}

.nav-wrap {
  width: min(calc(100% - 32px), var(--max-width));
  min-height: 72px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  flex: 0 0 auto;
  font-weight: 900;
  font-size: 21px;
}

.brand img {
  width: 42px;
  height: 42px;
  border: 2px solid var(--ink);
}

.brand span {
  line-height: 1;
}

.site-nav {
  display: flex;
  align-items: center;
  gap: 6px;
}

.site-nav > a:not(.download-btn) {
  padding: 8px 12px;
  border-bottom: 3px solid transparent;
  font-weight: 700;
}

.site-nav > a:not(.download-btn):hover,
.site-nav > a[aria-current="page"]:not(.download-btn) {
  border-bottom-color: var(--coral);
}

.nav-toggle {
  width: 44px;
  height: 44px;
  display: none;
  place-items: center;
  border: 2px solid var(--ink);
  background: var(--paper);
  cursor: pointer;
}

.nav-toggle span,
.nav-toggle::before,
.nav-toggle::after {
  width: 20px;
  height: 2px;
  display: block;
  background: var(--ink);
  content: "";
  transition: transform 180ms ease, opacity 180ms ease;
}

.nav-toggle span {
  margin: 4px 0;
}

.nav-toggle[aria-expanded="true"]::before {
  transform: translateY(6px) rotate(45deg);
}

.nav-toggle[aria-expanded="true"] span {
  opacity: 0;
}

.nav-toggle[aria-expanded="true"]::after {
  transform: translateY(-6px) rotate(-45deg);
}

.download-btn {
  min-height: 44px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 9px 18px;
  border: 2px solid var(--ink);
  border-radius: 4px;
  color: var(--paper);
  background: var(--coral);
  box-shadow: 3px 3px 0 var(--ink);
  font-weight: 900;
  transition: transform 150ms ease, box-shadow 150ms ease, background 150ms ease;
}

.download-btn::before {
  content: "\2193";
  font-size: 20px;
  line-height: 1;
}

.download-btn:hover {
  background: var(--coral-dark);
  box-shadow: 1px 1px 0 var(--ink);
  transform: translate(2px, 2px);
}

.download-btn.light {
  color: var(--ink);
  background: var(--yellow);
}

.text-link {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  font-weight: 900;
  border-bottom: 2px solid currentColor;
}

.text-link::after {
  content: "\2192";
}

.hero {
  position: relative;
  overflow: hidden;
  border-bottom: 2px solid var(--ink);
  background: var(--soft);
}

.hero::before,
.hero::after {
  position: absolute;
  border: 2px solid var(--ink);
  content: "";
}

.hero::before {
  width: 110px;
  height: 32px;
  top: 96px;
  left: -24px;
  background: var(--yellow);
  transform: rotate(-8deg);
}

.hero::after {
  width: 88px;
  height: 88px;
  right: -36px;
  bottom: 90px;
  background: var(--mint);
  transform: rotate(15deg);
}

.hero-inner {
  width: min(calc(100% - 32px), var(--max-width));
  margin: 0 auto;
  padding: 66px 0 34px;
  text-align: center;
}

.eyebrow {
  display: inline-block;
  margin: 0 0 14px;
  padding: 3px 10px;
  border: 2px solid var(--ink);
  color: var(--ink);
  background: var(--yellow);
  font-size: 13px;
  font-weight: 900;
}

h1,
h2,
h3,
p {
  margin-top: 0;
}

h1,
h2,
h3 {
  line-height: 1.25;
  letter-spacing: 0;
}

h1 {
  max-width: 850px;
  margin-right: auto;
  margin-bottom: 18px;
  margin-left: auto;
  font-size: clamp(38px, 6vw, 72px);
  font-weight: 950;
}

.hero-copy {
  max-width: 780px;
  margin: 0 auto 24px;
  color: #34353c;
  font-size: 18px;
}

.hero-actions {
  display: flex;
  align-items: center;
  justify-content: center;
  flex-wrap: wrap;
  gap: 18px;
}

.hero-proof {
  margin-top: 20px;
  display: flex;
  justify-content: center;
  flex-wrap: wrap;
  gap: 10px;
}

.hero-proof span {
  padding: 4px 9px;
  border: 1px solid var(--ink);
  background: var(--paper);
  font-size: 13px;
  font-weight: 800;
}

.hero-screens {
  min-height: 236px;
  margin-top: 36px;
  display: flex;
  align-items: flex-end;
  justify-content: center;
  gap: 22px;
}

.hero-screens figure {
  width: min(27vw, 210px);
  margin: 0;
  padding: 8px;
  border: 2px solid var(--ink);
  border-radius: 8px 8px 0 0;
  background: var(--ink);
  box-shadow: var(--shadow);
}

.hero-screens figure:nth-child(1) {
  transform: rotate(-3deg) translateY(20px);
}

.hero-screens figure:nth-child(3) {
  transform: rotate(3deg) translateY(20px);
}

.hero-screens img {
  width: 100%;
  height: auto;
  max-width: 400px;
}

.section {
  padding: 78px 0;
}

.section.alt {
  border-top: 2px solid var(--ink);
  border-bottom: 2px solid var(--ink);
  background: var(--soft);
}

.container {
  width: min(calc(100% - 32px), var(--max-width));
  margin: 0 auto;
}

.section-title {
  margin-bottom: 30px;
  display: flex;
  align-items: flex-end;
  justify-content: space-between;
  gap: 24px;
}

.section-title h2 {
  margin-bottom: 0;
  font-size: clamp(29px, 4vw, 46px);
}

.section-index {
  flex: 0 0 auto;
  color: var(--coral);
  font-weight: 950;
  font-size: 18px;
}

.feature-grid {
  display: grid;
  grid-template-columns: repeat(4, minmax(0, 1fr));
  gap: 18px;
}

.feature-card,
.topic-card,
.review,
.fact-card {
  border: 2px solid var(--ink);
  border-radius: 6px;
  background: var(--paper);
}

.feature-card {
  min-height: 260px;
  padding: 24px;
  box-shadow: 4px 4px 0 var(--ink);
}

.feature-card:nth-child(2) {
  border-top: 8px solid var(--mint);
}

.feature-card:nth-child(3) {
  border-top: 8px solid var(--yellow);
}

.feature-card:nth-child(4) {
  border-top: 8px solid var(--coral);
}

.feature-no {
  width: 40px;
  height: 40px;
  margin-bottom: 22px;
  display: grid;
  place-items: center;
  border: 2px solid var(--ink);
  border-radius: 50%;
  color: var(--paper);
  background: var(--ink);
  font-weight: 900;
}

.feature-card h3 {
  margin-bottom: 10px;
  font-size: 21px;
}

.feature-card p,
.topic-card p,
.fact-card p,
.review p {
  color: var(--muted);
}

.feature-card p:last-child,
.topic-card p:last-child,
.fact-card p:last-child,
.review p:last-child {
  margin-bottom: 0;
}

.reading-flow {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  border: 2px solid var(--ink);
}

.flow-step {
  min-height: 180px;
  padding: 24px;
  position: relative;
  background: var(--paper);
}

.flow-step + .flow-step {
  border-left: 2px solid var(--ink);
}

.flow-step strong {
  display: block;
  margin-bottom: 12px;
  font-size: 20px;
}

.flow-step b {
  display: block;
  margin-bottom: 18px;
  color: var(--coral);
  font-size: 13px;
}

.flow-step p {
  margin: 0;
  color: var(--muted);
}

.preview-layout {
  display: grid;
  grid-template-columns: 0.8fr 1.2fr;
  gap: 52px;
  align-items: center;
}

.preview-copy h2 {
  margin-bottom: 24px;
  font-size: clamp(30px, 4vw, 48px);
}

.preview-copy ul {
  margin: 0 0 28px;
  padding: 0;
  list-style: none;
}

.preview-copy li {
  padding: 13px 0;
  border-bottom: 1px solid #c9cbd0;
  font-weight: 800;
}

.preview-copy li::before {
  margin-right: 10px;
  color: var(--coral);
  content: "\25A0";
}

.preview-gallery {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 14px;
  align-items: end;
}

.preview-gallery figure {
  margin: 0;
}

.preview-gallery img {
  width: 100%;
  height: auto;
  max-width: 400px;
  border: 5px solid var(--ink);
  border-radius: 8px;
  box-shadow: 4px 4px 0 var(--coral);
}

.preview-gallery figcaption {
  padding: 10px 4px 0;
  font-size: 13px;
  font-weight: 900;
  text-align: center;
}

.topic-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 20px;
}

.topic-card {
  min-height: 260px;
  padding: 30px;
  position: relative;
  overflow: hidden;
}

.topic-card::after {
  width: 54px;
  height: 54px;
  position: absolute;
  right: -14px;
  bottom: -14px;
  border: 2px solid var(--ink);
  background: var(--yellow);
  content: "";
  transform: rotate(18deg);
}

.topic-card:nth-child(2)::after {
  background: var(--mint);
}

.topic-card .label {
  color: var(--coral);
  font-size: 13px;
  font-weight: 900;
}

.topic-card h3 {
  margin: 12px 0;
  font-size: 27px;
}

.stats-row {
  margin-bottom: 30px;
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  border: 2px solid var(--ink);
}

.stat {
  padding: 22px;
  text-align: center;
}

.stat + .stat {
  border-left: 2px solid var(--ink);
}

.stat strong {
  display: block;
  font-size: 30px;
}

.stat span {
  color: var(--muted);
  font-size: 13px;
  font-weight: 800;
}

.review-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 18px;
}

.review {
  padding: 24px;
}

.stars {
  margin-bottom: 13px;
  color: #b56a00;
  font-weight: 900;
}

.review footer {
  font-weight: 900;
}

.faq-list {
  border-top: 2px solid var(--ink);
}

.faq-list details {
  border-bottom: 2px solid var(--ink);
  background: var(--paper);
}

.faq-list summary {
  padding: 20px 50px 20px 4px;
  position: relative;
  cursor: pointer;
  font-weight: 900;
  list-style: none;
}

.faq-list summary::-webkit-details-marker {
  display: none;
}

.faq-list summary::after {
  width: 28px;
  height: 28px;
  position: absolute;
  top: 17px;
  right: 4px;
  display: grid;
  place-items: center;
  border: 2px solid var(--ink);
  background: var(--yellow);
  content: "+";
  line-height: 1;
}

.faq-list details[open] summary::after {
  content: "\2212";
}

.faq-list details p,
.faq-list details ul {
  max-width: 900px;
  margin: 0;
  padding: 0 48px 20px 4px;
  color: var(--muted);
}

.faq-list details ul {
  padding-left: 24px;
}

.bottom-cta {
  padding: 52px 0;
  color: var(--paper);
  background: var(--ink);
}

.bottom-cta .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 28px;
}

.bottom-cta h2 {
  margin-bottom: 8px;
  font-size: clamp(27px, 4vw, 42px);
}

.bottom-cta .cta-note {
  margin-bottom: 0;
  color: #c9cbd0;
}

.site-footer {
  padding: 40px 0 24px;
  border-top: 8px solid var(--coral);
  background: var(--soft);
}

.footer-grid {
  display: grid;
  grid-template-columns: 1.4fr 1fr 1fr;
  gap: 36px;
}

.footer-grid h2,
.footer-grid h3 {
  margin-bottom: 14px;
  font-size: 17px;
}

.footer-grid p,
.footer-grid a {
  color: var(--muted);
  font-size: 14px;
}

.footer-links {
  display: grid;
  gap: 8px;
}

.footer-links a:hover {
  color: var(--coral-dark);
}

.disclaimer {
  margin: 28px 0 0;
  padding-top: 20px;
  border-top: 1px solid #c9cbd0;
  color: var(--muted);
  font-size: 13px;
}

.copyright {
  margin: 8px 0 0;
  color: var(--muted);
  font-size: 13px;
}

.subhero {
  padding: 64px 0;
  border-bottom: 2px solid var(--ink);
  background: var(--yellow);
}

.subhero.mint {
  background: var(--mint);
}

.subhero .container {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 280px;
  align-items: end;
  gap: 48px;
}

.subhero h1 {
  margin: 0 0 16px;
  font-size: clamp(37px, 6vw, 64px);
}

.subhero p {
  max-width: 760px;
  margin-bottom: 0;
  font-size: 18px;
}

.chapter-tag {
  padding: 22px;
  border: 2px solid var(--ink);
  background: var(--paper);
  box-shadow: var(--shadow);
  font-weight: 900;
}

.chapter-tag span {
  display: block;
  color: var(--coral);
  font-size: 13px;
}

.article-layout {
  display: grid;
  grid-template-columns: 230px minmax(0, 1fr);
  gap: 46px;
  align-items: start;
}

.side-index {
  position: sticky;
  top: 96px;
  border: 2px solid var(--ink);
  background: var(--paper);
}

.side-index strong {
  display: block;
  padding: 13px 16px;
  color: var(--paper);
  background: var(--ink);
}

.side-index a {
  display: block;
  padding: 10px 16px;
  border-top: 1px solid #d9dade;
  color: var(--muted);
  font-size: 14px;
  font-weight: 700;
}

.side-index a:hover {
  color: var(--coral-dark);
  background: #fff4f2;
}

.article-content section {
  margin-bottom: 58px;
  scroll-margin-top: 98px;
}

.article-content h2 {
  margin-bottom: 22px;
  padding-bottom: 12px;
  border-bottom: 4px solid var(--ink);
  font-size: clamp(27px, 4vw, 38px);
}

.article-content h3 {
  margin: 28px 0 10px;
  font-size: 22px;
}

.article-content p {
  color: #3e4047;
}

.step-stack {
  display: grid;
  gap: 20px;
}

.guide-step {
  display: grid;
  grid-template-columns: 72px minmax(0, 1fr);
  gap: 22px;
  padding: 24px;
  border: 2px solid var(--ink);
  border-radius: 6px;
  background: var(--paper);
  box-shadow: 4px 4px 0 var(--ink);
}

.guide-step .number {
  width: 64px;
  height: 64px;
  display: grid;
  place-items: center;
  border: 2px solid var(--ink);
  border-radius: 50%;
  color: var(--paper);
  background: var(--coral);
  font-size: 23px;
  font-weight: 950;
}

.guide-step h3 {
  margin-top: 0;
}

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

.notice {
  padding: 20px 22px;
  border: 2px solid var(--ink);
  border-left: 10px solid var(--coral);
  background: #fff7e0;
}

.notice strong {
  display: block;
  margin-bottom: 6px;
}

.check-grid,
.fact-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 18px;
}

.check-item {
  padding: 18px;
  border-bottom: 2px solid var(--ink);
  background: var(--soft);
}

.check-item strong {
  display: block;
  margin-bottom: 6px;
}

.check-item p {
  margin-bottom: 0;
}

.fact-card {
  padding: 24px;
}

.fact-card h3 {
  margin-top: 0;
}

.mini-route {
  display: flex;
  gap: 14px;
  align-items: flex-start;
}

.mini-route img {
  width: min(100%, 180px);
  height: auto;
  max-width: 400px;
  border: 3px solid var(--ink);
  border-radius: 6px;
}

.feature-deep {
  display: grid;
  gap: 18px;
}

.feature-row {
  display: grid;
  grid-template-columns: 190px minmax(0, 1fr);
  gap: 26px;
  padding: 25px 0;
  border-bottom: 2px solid var(--ink);
}

.feature-row h3 {
  margin: 0;
}

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

.callout-links {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 18px;
}

.callout-links a {
  min-height: 150px;
  padding: 22px;
  border: 2px solid var(--ink);
  background: var(--yellow);
  box-shadow: 4px 4px 0 var(--ink);
  font-weight: 900;
}

.callout-links a:nth-child(2) {
  background: var(--mint);
}

.callout-links span {
  display: block;
  margin-top: 10px;
  font-size: 14px;
  font-weight: 600;
}

.reveal {
  opacity: 0;
  transform: translateY(14px);
  transition: opacity 420ms ease, transform 420ms ease;
}

.reveal.visible {
  opacity: 1;
  transform: none;
}

@media (max-width: 900px) {
  .nav-toggle {
    display: grid;
  }

  .site-nav {
    position: fixed;
    top: 72px;
    right: 0;
    bottom: 0;
    left: 0;
    padding: 22px 16px;
    display: none;
    align-items: stretch;
    flex-direction: column;
    background: var(--paper);
  }

  .site-nav.open {
    display: flex;
  }

  .site-nav > a:not(.download-btn) {
    padding: 14px 4px;
    border-bottom: 1px solid #d9dade;
  }

  .site-nav .download-btn {
    margin-top: 14px;
  }

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

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

  .flow-step + .flow-step {
    border-left: 0;
  }

  .flow-step:nth-child(even) {
    border-left: 2px solid var(--ink);
  }

  .flow-step:nth-child(n + 3) {
    border-top: 2px solid var(--ink);
  }

  .preview-layout,
  .subhero .container,
  .article-layout {
    grid-template-columns: 1fr;
  }

  .side-index {
    position: static;
  }

  .side-index nav {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
  }

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

  .stat:nth-child(3) {
    border-top: 2px solid var(--ink);
    border-left: 0;
  }

  .stat:nth-child(4) {
    border-top: 2px solid var(--ink);
  }

  .footer-grid {
    grid-template-columns: 1fr 1fr;
  }
}

@media (max-width: 640px) {
  .hero::before,
  .hero::after {
    display: none;
  }

  .nav-wrap {
    min-height: 64px;
  }

  .site-nav {
    top: 64px;
  }

  .hero-inner {
    padding-top: 48px;
  }

  h1 {
    font-size: 40px;
  }

  .hero-copy {
    font-size: 16px;
  }

  .hero-screens {
    min-height: 180px;
    gap: 8px;
  }

  .hero-screens figure {
    width: 31%;
    padding: 4px;
    box-shadow: 3px 3px 0 var(--ink);
  }

  .section {
    padding: 56px 0;
  }

  .section-title {
    align-items: flex-start;
    flex-direction: column;
    gap: 8px;
  }

  .feature-grid,
  .topic-grid,
  .review-grid,
  .check-grid,
  .fact-grid,
  .callout-links {
    grid-template-columns: 1fr;
  }

  .reading-flow {
    grid-template-columns: 1fr;
  }

  .flow-step:nth-child(even) {
    border-left: 0;
  }

  .flow-step:nth-child(n + 2) {
    border-top: 2px solid var(--ink);
  }

  .preview-gallery {
    gap: 8px;
  }

  .preview-gallery img {
    border-width: 3px;
    box-shadow: 2px 2px 0 var(--coral);
  }

  .preview-gallery figcaption {
    font-size: 11px;
  }

  .bottom-cta .container {
    align-items: flex-start;
    flex-direction: column;
  }

  .footer-grid {
    grid-template-columns: 1fr;
  }

  .subhero {
    padding: 46px 0;
  }

  .subhero h1 {
    font-size: 39px;
  }

  .article-layout {
    gap: 30px;
  }

  .side-index nav {
    grid-template-columns: 1fr;
  }

  .guide-step {
    grid-template-columns: 1fr;
  }

  .feature-row {
    grid-template-columns: 1fr;
    gap: 8px;
  }

  .mini-route {
    flex-direction: column;
  }
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }

  *,
  *::before,
  *::after {
    transition-duration: 0.01ms !important;
  }

  .reveal {
    opacity: 1;
    transform: none;
  }
}