:root {
  --ink: #172033;
  --muted: #607086;
  --line: #dce5f3;
  --surface: #ffffff;
  --soft: #f4f8fc;
  --blue: #1e72ff;
  --cyan: #16b8e8;
  --green: #12b981;
  --amber: #f4b544;
  --navy: #0b1d3a;
  --radius: 8px;
  --header-h: 68px;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Microsoft YaHei", Arial, sans-serif;
  color: var(--ink);
  background: var(--surface);
  line-height: 1.65;
}

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

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

.section-anchor {
  scroll-margin-top: calc(var(--header-h) + 24px);
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 20;
  background: rgba(255, 255, 255, .94);
  border-bottom: 1px solid rgba(220, 229, 243, .85);
  backdrop-filter: blur(18px);
}

.header-inner {
  max-width: 1180px;
  min-height: var(--header-h);
  margin: 0 auto;
  padding: 0 24px;
  display: flex;
  align-items: center;
  gap: 28px;
}

.brand,
.footer-brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  font-weight: 800;
  color: var(--ink);
}

.brand img,
.footer-brand img {
  width: 40px;
  height: 40px;
  border-radius: 8px;
}

.desktop-nav {
  display: flex;
  gap: 26px;
  margin-left: auto;
  color: var(--muted);
  font-size: 15px;
}

.desktop-nav a:hover,
.site-footer a:hover {
  color: var(--blue);
}

.header-cta,
.primary-action,
.secondary-action,
.mobile-cta {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 44px;
  border-radius: 999px;
  font-weight: 800;
  white-space: nowrap;
}

.header-cta {
  padding: 0 18px;
  color: #fff;
  background: var(--ink);
}

.menu-button {
  display: none;
  width: 44px;
  height: 44px;
  border: 0;
  background: transparent;
  padding: 10px;
}

.menu-button span {
  display: block;
  height: 2px;
  margin: 5px 0;
  background: var(--ink);
}

.mobile-nav {
  display: none;
}

.hero {
  max-width: 1180px;
  margin: 0 auto;
  padding: 76px 24px 54px;
  display: grid;
  grid-template-columns: minmax(0, .95fr) minmax(420px, 1.05fr);
  gap: 40px;
  align-items: center;
}

.eyebrow {
  margin: 0 0 12px;
  color: var(--blue);
  font-size: 13px;
  font-weight: 900;
}

.hero h1 {
  margin: 0;
  max-width: 620px;
  font-size: clamp(46px, 7vw, 82px);
  line-height: 1.03;
  letter-spacing: 0;
}

.hero-summary {
  max-width: 610px;
  margin: 22px 0 0;
  color: var(--muted);
  font-size: 19px;
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 14px;
  margin-top: 30px;
}

.primary-action {
  padding: 0 24px;
  color: #fff;
  background: linear-gradient(135deg, var(--blue), var(--cyan));
  box-shadow: 0 18px 36px rgba(30, 114, 255, .26);
}

.primary-action.light {
  color: var(--ink);
  background: #fff;
  box-shadow: none;
}

.secondary-action {
  padding: 0 22px;
  color: var(--ink);
  background: var(--soft);
  border: 1px solid var(--line);
}

.hero-points {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin-top: 28px;
}

.hero-points span,
.network-pill {
  padding: 8px 12px;
  border: 1px solid var(--line);
  border-radius: 999px;
  color: var(--muted);
  background: #fff;
  font-size: 14px;
}

.hero-media {
  padding: 12px;
  border-radius: 28px;
  background: linear-gradient(145deg, #edf6ff, #ffffff 48%, #e7fff7);
  box-shadow: 0 28px 70px rgba(31, 48, 82, .16);
}

.hero-media img {
  border-radius: 18px;
  aspect-ratio: 16 / 9;
  object-fit: cover;
}

.core-summary,
.download-section,
.feature-section,
.guide-section,
.semantic-section,
.faq-section {
  padding: 72px 24px;
}

.core-summary,
.feature-section,
.semantic-section {
  background: var(--soft);
}

.section-head {
  max-width: 860px;
  margin: 0 auto 34px;
  text-align: center;
}

.section-head.compact {
  max-width: 760px;
}

.section-head h2,
.screen-copy h2,
.final-cta h2 {
  margin: 0;
  font-size: clamp(28px, 4vw, 44px);
  line-height: 1.18;
  letter-spacing: 0;
}

.section-head p:not(.eyebrow),
.screen-copy p,
.final-cta p {
  color: var(--muted);
  font-size: 17px;
}

.summary-grid,
.feature-grid {
  max-width: 1120px;
  margin: 0 auto;
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 18px;
}

.summary-grid article,
.feature-card,
.semantic-ring div {
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: #fff;
}

.summary-grid article {
  padding: 24px;
}

.summary-grid span {
  color: var(--green);
  font-weight: 900;
}

.summary-grid h3,
.feature-card h3,
.guide-list h3,
.semantic-ring dt {
  margin: 8px 0;
  font-size: 20px;
  line-height: 1.25;
}

.summary-grid p,
.feature-card p,
.guide-list p,
.semantic-ring dd,
.faq-answer p {
  margin: 0;
  color: var(--muted);
}

.download-layout {
  max-width: 1100px;
  margin: 0 auto;
  display: grid;
  grid-template-columns: minmax(0, 1fr) 420px;
  gap: 36px;
  align-items: center;
}

.download-cards {
  display: grid;
  gap: 16px;
}

.download-card {
  min-height: 118px;
  padding: 22px;
  display: grid;
  grid-template-columns: 72px 1fr;
  column-gap: 18px;
  align-items: center;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: #fff;
  box-shadow: 0 12px 28px rgba(31, 48, 82, .06);
}

.download-card:hover {
  border-color: var(--blue);
  transform: translateY(-2px);
}

.card-icon {
  grid-row: span 2;
  width: 64px;
  height: 64px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border-radius: 8px;
  color: #fff;
  background: var(--navy);
  font-weight: 900;
}

.download-card strong {
  font-size: 20px;
}

.download-card small {
  color: var(--muted);
  font-size: 14px;
}

.phone-stack {
  position: relative;
  min-height: 500px;
  margin: 0;
}

.phone-stack img {
  position: absolute;
  width: 220px;
  border-radius: 22px;
  box-shadow: 0 24px 52px rgba(31, 48, 82, .22);
}

.phone-a {
  top: 12px;
  left: 58px;
  z-index: 2;
}

.phone-b {
  top: 84px;
  right: 42px;
  opacity: .92;
}

.feature-card {
  overflow: hidden;
}

.feature-card img {
  width: 100%;
  aspect-ratio: 4 / 3;
  object-fit: cover;
  background: var(--soft);
}

.feature-card h3,
.feature-card p {
  padding-left: 20px;
  padding-right: 20px;
}

.feature-card h3 {
  margin-top: 20px;
}

.feature-card p {
  padding-bottom: 22px;
}

.screen-section {
  max-width: 1180px;
  margin: 0 auto;
  padding: 80px 24px;
  display: grid;
  grid-template-columns: minmax(0, .85fr) minmax(420px, 1.15fr);
  gap: 38px;
  align-items: center;
}

.plain-list {
  margin: 22px 0 0;
  padding: 0;
  display: grid;
  gap: 10px;
  list-style: none;
  color: var(--muted);
}

.plain-list li {
  padding-left: 18px;
  position: relative;
}

.plain-list li::before {
  content: "";
  position: absolute;
  left: 0;
  top: .75em;
  width: 7px;
  height: 7px;
  border-radius: 50%;
  background: var(--green);
}

.screen-media {
  display: grid;
  grid-template-columns: 1fr 160px;
  gap: 16px;
  align-items: end;
}

.screen-media img {
  border-radius: 18px;
  box-shadow: 0 20px 42px rgba(31, 48, 82, .14);
}

.screen-media img:first-child {
  aspect-ratio: 16 / 9;
  object-fit: cover;
}

.screen-media img:last-child {
  aspect-ratio: 9 / 16;
  object-fit: cover;
}

.guide-list {
  max-width: 880px;
  margin: 0 auto;
  display: grid;
  gap: 14px;
}

.guide-list article {
  display: grid;
  grid-template-columns: 58px 1fr;
  gap: 18px;
  align-items: start;
  padding: 20px;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: #fff;
}

.guide-list span {
  width: 48px;
  height: 48px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border-radius: 8px;
  color: #fff;
  background: var(--blue);
  font-weight: 900;
}

.semantic-ring {
  max-width: 1120px;
  margin: 0 auto;
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 16px;
}

.semantic-ring div {
  padding: 20px;
}

.semantic-ring dt {
  font-weight: 900;
}

.semantic-ring dd {
  margin: 0;
  font-size: 14px;
}

.faq-list {
  max-width: 820px;
  margin: 0 auto;
  display: grid;
  gap: 12px;
}

.faq-item {
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: #fff;
  overflow: hidden;
}

.faq-question {
  width: 100%;
  min-height: 58px;
  padding: 16px 20px;
  border: 0;
  background: #fff;
  color: var(--ink);
  cursor: pointer;
  font: inherit;
  font-weight: 850;
  text-align: left;
  display: flex;
  justify-content: space-between;
  gap: 16px;
}

.faq-question::after {
  content: "+";
  color: var(--blue);
  font-size: 24px;
  line-height: 1;
}

.faq-item.is-open .faq-question::after {
  content: "-";
}

.faq-answer {
  display: none;
  padding: 0 20px 18px;
}

.faq-item.is-open .faq-answer {
  display: block;
}

.final-cta {
  max-width: 1120px;
  margin: 0 auto 72px;
  padding: 34px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
  border-radius: 18px;
  color: #fff;
  background: linear-gradient(135deg, var(--navy), #104eb2 62%, var(--green));
}

.final-cta .eyebrow,
.final-cta p {
  color: rgba(255, 255, 255, .82);
}

.site-footer {
  padding: 38px 24px 78px;
  border-top: 1px solid var(--line);
  background: #fff;
  text-align: center;
}

.site-footer .footer-brand {
  justify-content: center;
}

.site-footer nav {
  display: flex;
  justify-content: center;
  flex-wrap: wrap;
  gap: 18px;
  margin: 22px 0 12px;
  color: var(--muted);
  font-size: 14px;
}

.footer-help {
  display: flex;
  justify-content: center;
  margin: 18px 0 16px;
}

.footer-help-button {
  min-width: 132px;
  min-height: 44px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 11px 22px;
  border-radius: 999px;
  color: #fff;
  background: linear-gradient(135deg, var(--blue), var(--cyan) 58%, var(--green));
  box-shadow: 0 12px 28px rgba(30, 114, 255, .22);
  font-size: 15px;
  font-weight: 900;
}

.footer-help-button:hover {
  transform: translateY(-1px);
  box-shadow: 0 16px 34px rgba(30, 114, 255, .28);
}

.site-footer p {
  margin: 0;
  color: var(--muted);
  font-size: 13px;
}

.floating-download {
  position: fixed;
  right: 18px;
  bottom: 18px;
  z-index: 15;
  min-width: 112px;
  min-height: 46px;
  padding: 0 18px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border-radius: 999px;
  color: #fff;
  background: var(--ink);
  box-shadow: 0 14px 28px rgba(23, 32, 51, .24);
  font-weight: 900;
}

.back-top {
  position: fixed;
  right: 154px;
  bottom: 18px;
  z-index: 15;
  width: 46px;
  height: 46px;
  border: 1px solid var(--line);
  border-radius: 50%;
  color: var(--ink);
  background: #fff;
  box-shadow: 0 12px 26px rgba(31, 48, 82, .16);
  cursor: pointer;
  opacity: 0;
  visibility: hidden;
}

.back-top.is-visible {
  opacity: 1;
  visibility: visible;
}

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

@media (max-width: 980px) {
  .desktop-nav,
  .header-cta {
    display: none;
  }

  .header-inner {
    justify-content: space-between;
  }

  .menu-button {
    display: block;
  }

  .mobile-nav {
    display: none;
    padding: 12px 24px 20px;
    border-top: 1px solid var(--line);
    background: #fff;
  }

  .mobile-nav.is-open {
    display: grid;
    gap: 8px;
  }

  .mobile-nav a {
    min-height: 44px;
    display: flex;
    align-items: center;
    color: var(--muted);
  }

  .mobile-cta {
    justify-content: center;
    color: #fff !important;
    background: var(--ink);
  }

  .hero,
  .screen-section,
  .download-layout {
    grid-template-columns: 1fr;
  }

  .hero {
    padding-top: 46px;
  }

  .download-layout {
    gap: 18px;
  }

  .phone-stack {
    min-height: 430px;
    max-width: 420px;
    margin: 0 auto;
    width: 100%;
  }

  .phone-a {
    left: 22px;
  }

  .phone-b {
    right: 20px;
  }

  .summary-grid,
  .feature-grid,
  .semantic-ring {
    grid-template-columns: 1fr 1fr;
  }
}

@media (max-width: 680px) {
  :root {
    --header-h: 62px;
  }

  .header-inner,
  .hero,
  .core-summary,
  .download-section,
  .feature-section,
  .guide-section,
  .semantic-section,
  .faq-section,
  .screen-section {
    padding-left: 16px;
    padding-right: 16px;
  }

  .brand img {
    width: 34px;
    height: 34px;
  }

  .hero h1 {
    font-size: 40px;
  }

  .hero-summary,
  .section-head p:not(.eyebrow),
  .screen-copy p,
  .final-cta p {
    font-size: 16px;
  }

  .summary-grid,
  .feature-grid,
  .semantic-ring,
  .screen-media {
    grid-template-columns: 1fr;
  }

  .download-card {
    grid-template-columns: 58px 1fr;
    min-height: 106px;
    padding: 18px;
  }

  .card-icon {
    width: 52px;
    height: 52px;
    font-size: 13px;
  }

  .phone-stack {
    min-height: 390px;
  }

  .phone-stack img {
    width: 190px;
  }

  .screen-media img:last-child {
    max-width: 220px;
    margin: 0 auto;
  }

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

  .final-cta {
    margin-left: 16px;
    margin-right: 16px;
    flex-direction: column;
    align-items: flex-start;
    padding: 26px;
  }

  .footer-help-button {
    width: min(100%, 220px);
  }

  .floating-download {
    right: 14px;
    bottom: 14px;
  }

  .back-top {
    right: 146px;
    bottom: 14px;
  }
}

@media (max-width: 420px) {
  .hero-points {
    display: grid;
  }

  .phone-stack {
    min-height: 320px;
  }

  .phone-stack img {
    width: 158px;
  }

  .phone-b {
    top: 72px;
  }
}