:root {
  --red: #d71920;
  --red-dark: #aa1016;
  --black: #131313;
  --ink: #282828;
  --muted: #686868;
  --paper: #ffffff;
  --soft: #f4f4f4;
  --soft-red: #fff1f1;
  --line: #dddddd;
  --white: #ffffff;
  --shell: 1180px;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
  scroll-padding-top: 82px;
}

body {
  margin: 0;
  min-width: 320px;
  color: var(--ink);
  background: var(--paper);
  font-family: Arial, "Microsoft YaHei", "PingFang SC", "Segoe UI", sans-serif;
  line-height: 1.75;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

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

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

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

button {
  font: inherit;
}

.skip-link {
  position: fixed;
  top: -90px;
  left: 18px;
  z-index: 1000;
  padding: 10px 15px;
  color: var(--white);
  background: var(--black);
  font-weight: 800;
}

.skip-link:focus {
  top: 18px;
}

.header-shell,
.hero-shell,
.section-shell,
.final-shell,
.footer-shell {
  width: min(calc(100% - 40px), var(--shell));
  margin-inline: auto;
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(255, 255, 255, 0.97);
  border-bottom: 1px solid var(--line);
  backdrop-filter: blur(12px);
}

.header-shell {
  min-height: 76px;
  display: grid;
  grid-template-columns: 210px 1fr 180px;
  gap: 28px;
  align-items: center;
}

.brand {
  width: max-content;
}

.brand img,
.footer-brand img {
  width: auto;
  height: 38px;
  object-fit: contain;
}

.site-nav {
  display: flex;
  justify-content: center;
  gap: 30px;
  color: #5f5f5f;
  font-size: 13px;
  font-weight: 700;
}

.site-nav a {
  padding: 24px 0 22px;
}

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

.header-download {
  justify-self: end;
  padding: 11px 15px;
  color: var(--white);
  background: var(--red);
  text-align: center;
  font-size: 13px;
  font-weight: 800;
}

.header-download:hover,
.header-download:focus-visible {
  background: var(--red-dark);
}

.menu-button {
  display: none;
  width: 44px;
  height: 44px;
  background: var(--white);
  border: 1px solid var(--line);
  cursor: pointer;
}

.menu-button span {
  display: block;
  width: 19px;
  height: 2px;
  margin: 4px auto;
  background: var(--black);
}

.hero {
  padding: 88px 0 72px;
  background: var(--soft);
  border-bottom: 1px solid var(--line);
}

.hero-shell {
  display: grid;
  grid-template-columns: 1.05fr 0.95fr;
  gap: 64px;
  align-items: center;
}

.eyebrow,
.section-label {
  margin: 0 0 14px;
  color: var(--red);
  font-size: 11px;
  font-weight: 900;
  letter-spacing: 0.14em;
  text-transform: uppercase;
}

.hero h1 {
  margin: 0;
  color: var(--black);
  font-size: clamp(48px, 6vw, 78px);
  line-height: 1.05;
  letter-spacing: -0.045em;
}

.hero-lead {
  max-width: 700px;
  margin: 27px 0 0;
  color: #555;
  font-size: 18px;
  line-height: 1.9;
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 13px;
  margin-top: 31px;
}

.button {
  min-height: 54px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 20px;
  padding: 13px 20px;
  border: 1px solid transparent;
  font-weight: 800;
}

.button-primary {
  min-width: 235px;
  color: var(--white);
  background: var(--red);
}

.button-primary:hover,
.button-primary:focus-visible {
  background: var(--red-dark);
}

.button-primary b {
  font-size: 19px;
}

.button-secondary {
  color: var(--black);
  background: var(--white);
  border-color: var(--line);
}

.button-secondary:hover,
.button-secondary:focus-visible {
  border-color: #999;
}

.hero-points {
  display: flex;
  flex-wrap: wrap;
  gap: 9px;
  margin-top: 28px;
}

.hero-points span {
  padding: 7px 10px;
  color: #555;
  background: var(--white);
  border: 1px solid var(--line);
  font-size: 11px;
  font-weight: 700;
}

.hero-visual {
  padding: 20px;
  background: var(--white);
  border: 1px solid var(--line);
}

.hero-visual img {
  width: 100%;
  max-height: 410px;
  object-fit: contain;
}

.section {
  padding: 94px 0;
}

.section-heading {
  max-width: 850px;
}

.section-heading h2,
.purpose-title h2,
.precheck-copy h2,
.problems-heading h2,
.faq-heading h2,
.final-shell h2 {
  margin: 0;
  color: var(--black);
  font-size: clamp(31px, 4vw, 48px);
  line-height: 1.2;
  letter-spacing: -0.035em;
}

.section-heading > p:not(.section-label),
.problems-heading > p:not(.section-label),
.faq-heading > p:not(.section-label) {
  margin: 19px 0 0;
  color: var(--muted);
}

.quick-download {
  background: var(--paper);
}

.download-list {
  margin-top: 43px;
  border-top: 2px solid var(--black);
}

.download-list article {
  display: grid;
  grid-template-columns: 64px 1fr 150px;
  gap: 25px;
  align-items: center;
  min-height: 150px;
  padding: 23px 0;
  border-bottom: 1px solid var(--line);
}

.platform-mark {
  width: 52px;
  height: 52px;
  display: grid;
  place-items: center;
  color: var(--white);
  background: var(--black);
  font-size: 18px;
  font-weight: 900;
}

.download-list article:nth-child(2) .platform-mark {
  background: var(--red);
}

.platform-copy > span {
  color: var(--red);
  font-size: 10px;
  font-weight: 900;
  letter-spacing: 0.08em;
}

.platform-copy h3 {
  margin: 4px 0 7px;
  color: var(--black);
  font-size: 20px;
}

.platform-copy p {
  margin: 0;
  color: var(--muted);
}

.platform-button {
  min-height: 46px;
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--white);
  background: var(--red);
  font-size: 12px;
  font-weight: 800;
}

.platform-button:hover,
.platform-button:focus-visible {
  background: var(--red-dark);
}

.purpose-section {
  background: var(--black);
  color: var(--white);
}

.purpose-layout {
  display: grid;
  grid-template-columns: 0.6fr 1.4fr;
  gap: 80px;
  align-items: start;
}

.purpose-title h2 {
  color: var(--white);
}

.purpose-lead {
  margin: 0;
  color: #eee;
  font-size: 21px;
  font-weight: 700;
  line-height: 1.65;
}

.purpose-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  margin-top: 30px;
  border-top: 1px solid #373737;
  border-left: 1px solid #373737;
}

.purpose-grid article {
  min-height: 215px;
  padding: 24px;
  border-right: 1px solid #373737;
  border-bottom: 1px solid #373737;
}

.purpose-grid b {
  color: var(--red);
  font-size: 11px;
}

.purpose-grid h3 {
  margin: 35px 0 9px;
  font-size: 18px;
}

.purpose-grid p {
  margin: 0;
  color: #aaa;
  font-size: 13px;
}

.devices-section {
  background: var(--soft);
}

.device-table {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  margin-top: 43px;
  border-top: 1px solid var(--line);
  border-left: 1px solid var(--line);
}

.device-table article {
  min-height: 300px;
  padding: 27px;
  background: var(--white);
  border-right: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
}

.device-table span {
  color: var(--red);
  font-size: 10px;
  font-weight: 900;
  letter-spacing: 0.1em;
}

.device-table h3 {
  margin: 40px 0 11px;
  color: var(--black);
  font-size: 20px;
}

.device-table p {
  margin: 0;
  color: var(--muted);
}

.device-table strong {
  display: block;
  margin-top: 22px;
  padding-top: 18px;
  color: #444;
  border-top: 1px solid var(--line);
  font-size: 12px;
}

.precheck-section {
  background: var(--paper);
}

.precheck-layout {
  display: grid;
  grid-template-columns: 1.1fr 0.9fr;
  gap: 65px;
  align-items: center;
}

.precheck-list {
  margin: 35px 0 0;
  padding: 0;
  list-style: none;
  border-top: 2px solid var(--black);
}

.precheck-list li {
  display: grid;
  grid-template-columns: 45px 1fr;
  gap: 18px;
  padding: 21px 0;
  border-bottom: 1px solid var(--line);
}

.precheck-list li > b {
  color: var(--red);
  font-size: 11px;
}

.precheck-list h3 {
  margin: -4px 0 7px;
  color: var(--black);
  font-size: 18px;
}

.precheck-list p {
  margin: 0;
  color: var(--muted);
}

.precheck-visual {
  margin: 0;
  padding: 18px;
  background: var(--soft);
  border: 1px solid var(--line);
}

.precheck-visual img {
  width: 100%;
  max-height: 430px;
  object-fit: contain;
}

.precheck-visual figcaption {
  margin-top: 13px;
  color: #777;
  font-size: 11px;
}

.steps-section {
  background: var(--black);
  color: var(--white);
}

.section-heading-light h2 {
  color: var(--white);
}

.section-heading-light > p:not(.section-label) {
  color: #aaa;
}

.steps-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  margin: 43px 0 0;
  padding: 0;
  list-style: none;
  border-top: 1px solid #393939;
  border-left: 1px solid #393939;
}

.steps-grid li {
  min-height: 255px;
  padding: 24px;
  border-right: 1px solid #393939;
  border-bottom: 1px solid #393939;
}

.steps-grid span {
  color: var(--red);
  font-size: 11px;
  font-weight: 900;
}

.steps-grid h3 {
  margin: 55px 0 10px;
  font-size: 18px;
}

.steps-grid p {
  margin: 0;
  color: #aaa;
  font-size: 13px;
}

.steps-action {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 25px;
  margin-top: 22px;
  padding: 22px 25px;
  color: var(--black);
  background: var(--white);
}

.steps-action strong,
.steps-action span {
  display: block;
}

.steps-action strong {
  font-size: 16px;
}

.steps-action span {
  color: #666;
  font-size: 11px;
}

.steps-action a {
  min-width: 135px;
  padding: 11px 16px;
  color: var(--white);
  background: var(--red);
  text-align: center;
  font-size: 12px;
  font-weight: 800;
}

.problems-section {
  background: var(--paper);
}

.problems-layout {
  display: grid;
  grid-template-columns: 0.58fr 1.42fr;
  gap: 75px;
  align-items: start;
}

.problems-heading {
  position: sticky;
  top: 110px;
}

.problems-list {
  border-top: 2px solid var(--black);
}

.problems-list article {
  display: grid;
  grid-template-columns: 90px 1fr 1.15fr;
  gap: 23px;
  padding: 24px 0;
  border-bottom: 1px solid var(--line);
}

.problems-list span {
  color: var(--red);
  font-size: 10px;
  font-weight: 900;
}

.problems-list h3 {
  margin: -4px 0 0;
  color: var(--black);
  font-size: 18px;
  line-height: 1.45;
}

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

.faq-section {
  background: var(--soft-red);
}

.faq-layout {
  display: grid;
  grid-template-columns: 0.65fr 1.35fr;
  gap: 75px;
  align-items: start;
}

.faq-heading {
  position: sticky;
  top: 110px;
}

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

.faq-list details {
  border-bottom: 1px solid #e1caca;
}

.faq-list summary {
  position: relative;
  padding: 23px 55px 23px 0;
  color: var(--black);
  font-size: 16px;
  font-weight: 800;
  cursor: pointer;
  list-style: none;
}

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

.faq-list summary span {
  position: absolute;
  right: 3px;
  top: 20px;
  width: 30px;
  height: 30px;
  display: grid;
  place-items: center;
  color: var(--red);
  border: 1px solid #d9bcbc;
  border-radius: 50%;
  transition: transform 0.2s ease;
}

.faq-list details[open] summary span {
  transform: rotate(45deg);
}

.faq-list details p {
  margin: -2px 0 23px;
  color: var(--muted);
}

.related-section {
  background: var(--paper);
}

.related-list {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  margin-top: 42px;
  border-top: 1px solid var(--line);
  border-left: 1px solid var(--line);
}

.related-list a {
  min-height: 130px;
  display: grid;
  align-content: center;
  padding: 23px;
  border-right: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
}

.related-list a:last-child {
  grid-column: 1 / -1;
}

.related-list a:hover,
.related-list a:focus-visible {
  background: var(--soft);
}

.related-list strong {
  color: var(--red);
  font-size: 16px;
}

.related-list span {
  margin-top: 5px;
  color: var(--muted);
  font-size: 12px;
}

.final-section {
  padding: 0 0 90px;
  background: var(--paper);
}

.final-shell {
  min-height: 245px;
  display: grid;
  grid-template-columns: 1fr 240px;
  gap: 50px;
  align-items: center;
  padding: 43px 50px;
  color: var(--white);
  background: var(--red);
}

.final-shell p {
  margin: 0 0 10px;
  color: #ffd4d5;
  font-size: 10px;
  font-weight: 900;
  letter-spacing: 0.13em;
}

.final-shell h2 {
  color: var(--white);
}

.final-shell > div > span {
  display: block;
  margin-top: 13px;
  color: #ffe5e5;
  font-size: 12px;
}

.final-button {
  min-height: 68px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 18px;
  padding: 16px 20px;
  color: var(--black);
  background: var(--white);
  font-weight: 900;
}

.final-button b {
  font-size: 20px;
}

.site-footer {
  padding: 52px 0 32px;
  color: #aaa;
  background: var(--black);
}

.footer-shell {
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 32px 55px;
  align-items: start;
}

.footer-brand img {
  filter: brightness(0) invert(1);
}

.footer-brand p {
  max-width: 720px;
  margin: 17px 0 0;
  color: #777;
  font-size: 11px;
}

.footer-nav {
  display: grid;
  grid-template-columns: repeat(2, auto);
  gap: 8px 25px;
  font-size: 12px;
  font-weight: 700;
}

.footer-nav a:hover,
.footer-nav a:focus-visible {
  color: var(--white);
}

.copyright {
  grid-column: 1 / -1;
  margin: 5px 0 0;
  padding-top: 21px;
  color: #555;
  border-top: 1px solid #2c2c2c;
  font-size: 11px;
}

.mobile-download {
  display: none;
}

@media (max-width: 920px) {
  .header-shell {
    grid-template-columns: 190px 1fr 175px;
  }

  .site-nav {
    gap: 18px;
  }

  .hero-shell,
  .purpose-layout,
  .precheck-layout,
  .problems-layout,
  .faq-layout {
    gap: 45px;
  }

  .problems-list article {
    grid-template-columns: 80px 1fr;
  }

  .problems-list p {
    grid-column: 2;
  }
}

@media (max-width: 800px) {
  html {
    scroll-padding-top: 72px;
  }

  .header-shell {
    min-height: 70px;
    grid-template-columns: 1fr auto;
  }

  .brand img {
    height: 34px;
  }

  .header-download {
    display: none;
  }

  .menu-button {
    display: block;
  }

  .site-nav {
    position: absolute;
    left: 20px;
    right: 20px;
    top: calc(100% + 8px);
    display: none;
    padding: 9px;
    background: var(--white);
    border: 1px solid var(--line);
    box-shadow: 0 20px 50px rgba(0, 0, 0, 0.16);
  }

  .site-nav.is-open {
    display: grid;
  }

  .site-nav a {
    padding: 11px 12px;
  }

  .hero-shell,
  .purpose-layout,
  .precheck-layout,
  .problems-layout,
  .faq-layout {
    grid-template-columns: 1fr;
  }

  .hero-copy {
    text-align: center;
  }

  .hero-actions,
  .hero-points {
    justify-content: center;
  }

  .hero-visual {
    max-width: 650px;
    margin-inline: auto;
  }

  .device-table {
    grid-template-columns: 1fr;
  }

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

  .problems-heading,
  .faq-heading {
    position: static;
  }

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

  .related-list a:last-child {
    grid-column: auto;
  }

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

  .copyright {
    grid-column: auto;
  }
}

@media (max-width: 600px) {
  body {
    padding-bottom: 70px;
  }

  .header-shell,
  .hero-shell,
  .section-shell,
  .final-shell,
  .footer-shell {
    width: min(calc(100% - 28px), var(--shell));
  }

  .hero {
    padding: 60px 0 55px;
  }

  .hero h1 {
    font-size: clamp(42px, 13vw, 60px);
  }

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

  .hero-actions {
    display: grid;
  }

  .button {
    width: 100%;
  }

  .section {
    padding: 68px 0;
  }

  .section-heading h2,
  .purpose-title h2,
  .precheck-copy h2,
  .problems-heading h2,
  .faq-heading h2 {
    font-size: clamp(29px, 9vw, 39px);
  }

  .download-list article {
    grid-template-columns: 52px 1fr;
    gap: 15px;
  }

  .platform-button {
    grid-column: 2;
    width: 150px;
  }

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

  .purpose-grid article {
    min-height: 0;
  }

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

  .steps-grid li {
    min-height: 0;
  }

  .steps-grid h3 {
    margin-top: 30px;
  }

  .steps-action {
    display: grid;
  }

  .steps-action a {
    width: 100%;
  }

  .problems-list article {
    grid-template-columns: 1fr;
    gap: 7px;
  }

  .problems-list p {
    grid-column: auto;
  }

  .faq-list summary {
    font-size: 15px;
  }

  .final-section {
    padding-bottom: 65px;
  }

  .final-shell {
    grid-template-columns: 1fr;
    padding: 35px 23px;
  }

  .final-button {
    width: 100%;
  }

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

  .mobile-download {
    position: fixed;
    left: 0;
    right: 0;
    bottom: 0;
    z-index: 120;
    min-height: 70px;
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 12px;
    padding: 9px 14px;
    color: var(--white);
    background: rgba(19, 19, 19, 0.97);
    border-top: 1px solid #333;
  }

  .mobile-download > div {
    min-width: 0;
    display: flex;
    align-items: center;
    gap: 10px;
  }

  .mobile-download img {
    width: 44px;
    height: 44px;
    object-fit: contain;
    border-radius: 10px;
  }

  .mobile-download small,
  .mobile-download strong {
    display: block;
    line-height: 1.2;
  }

  .mobile-download small {
    color: #777;
    font-size: 10px;
  }

  .mobile-download strong {
    margin-top: 3px;
    font-size: 13px;
  }

  .mobile-download > a {
    flex: 0 0 auto;
    padding: 11px 15px;
    color: var(--white);
    background: var(--red);
    font-size: 13px;
    font-weight: 900;
  }
}

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

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