:root {
  --blue: #3370ff;
  --blue-dark: #245bdb;
  --text: #1f2329;
  --muted: #646a73;
  --line: #e8ebf0;
  --bg: #ffffff;
  --footer: #0f1728;
}

* {
  box-sizing: border-box;
}

html,
body {
  margin: 0;
  min-height: 100%;
  background: var(--bg);
  color: var(--text);
  font-family: Inter, -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Microsoft YaHei", sans-serif;
  -webkit-font-smoothing: antialiased;
}

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

button {
  font: inherit;
  border: 0;
  background: none;
  cursor: pointer;
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 14px 18px;
  background: rgba(255, 255, 255, 0.94);
  backdrop-filter: blur(10px);
}

.brand,
.footer-brand {
  display: inline-flex;
  align-items: center;
}

.brand-logo {
  display: block;
  height: 28px;
  width: auto;
}

.footer-logo {
  display: block;
  height: 88px;
  width: auto;
  margin: 0 auto;
}

.web-entry {
  padding: 8px 16px;
  border: 1px solid #d7dbe3;
  border-radius: 999px;
  color: var(--muted);
  font-size: 0.88rem;
  font-weight: 500;
}

.hero {
  padding: 18px 18px 56px;
  text-align: center;
}

.hero-visual {
  margin-bottom: 28px;
}

.hero-image {
  display: block;
  width: min(100%, 360px);
  height: auto;
  margin: 0 auto;
}

.hero h1 {
  margin: 0 0 16px;
  font-size: clamp(1.8rem, 7vw, 2.4rem);
  line-height: 1.2;
  font-weight: 800;
  letter-spacing: -0.03em;
}

.hero h1 span {
  color: var(--blue);
}

.hero-desc {
  margin: 0 auto 24px;
  max-width: 520px;
  color: var(--muted);
  font-size: 0.95rem;
  line-height: 1.75;
}

.btn-primary {
  min-width: 180px;
  padding: 14px 34px;
  border-radius: 999px;
  background: var(--blue);
  color: #fff;
  font-size: 1rem;
  font-weight: 700;
  box-shadow: 0 12px 28px rgba(51, 112, 255, 0.28);
  transition: background 0.2s ease, transform 0.2s ease;
}

.btn-primary:hover {
  background: var(--blue-dark);
  transform: translateY(-1px);
}

.features,
.sdk,
.download {
  padding: 48px 18px;
  text-align: center;
}

.features h2,
.sdk h2,
.download h2 {
  margin: 0 0 28px;
  font-size: clamp(1.5rem, 5.5vw, 2rem);
  font-weight: 800;
  letter-spacing: -0.03em;
}

.feature-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 36px 12px;
}

.feature-card {
  max-width: none;
  margin: 0;
}

.feature-icon {
  width: 112px;
  height: 112px;
  margin: 0 auto 14px;
  display: grid;
  place-items: center;
}

.feature-icon img {
  display: block;
  width: 100%;
  height: 100%;
  object-fit: contain;
}

.feature-card h3 {
  margin: 0 0 8px;
  font-size: 0.95rem;
  font-weight: 700;
}

.feature-card p {
  margin: 0;
  color: var(--muted);
  font-size: 0.78rem;
  line-height: 1.55;
}

.sdk {
  background: linear-gradient(180deg, #fafbfd 0%, #f4f7fb 100%);
}

.sdk p {
  margin: 0 auto 24px;
  max-width: 560px;
  color: var(--muted);
  font-size: 0.95rem;
  line-height: 1.75;
}

.sdk-actions {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 14px;
}

.btn-sdk {
  min-width: 150px;
  padding: 13px 28px;
  border-radius: 999px;
  background: var(--blue);
  color: #fff;
  font-size: 0.95rem;
  font-weight: 700;
}

.btn-sdk:hover {
  background: var(--blue-dark);
}

.platform-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 16px;
  max-width: 420px;
  margin: 0 auto;
}

.platform-card {
  padding: 22px 16px 18px;
  border-radius: 16px;
  background: #fff;
  border: 1px solid var(--line);
  box-shadow: 0 10px 30px rgba(31, 35, 41, 0.06);
}

.platform-card:nth-child(5) {
  grid-column: 1 / -1;
  width: min(100%, 190px);
  margin: 0 auto;
}

.platform-icon {
  width: 54px;
  height: 54px;
  margin: 0 auto 12px;
  display: grid;
  place-items: center;
}

.platform-icon img {
  display: block;
  width: 100%;
  height: 100%;
  object-fit: contain;
}

.platform-card h3 {
  margin: 0 0 16px;
  font-size: 1rem;
  font-weight: 600;
}

.platform-btn {
  width: 48px;
  height: 48px;
  margin: 0 auto;
  padding: 0;
  border-radius: 50%;
  background: transparent;
  display: grid;
  place-items: center;
  transition: transform 0.2s ease;
}

.platform-btn img {
  display: block;
  width: 100%;
  height: 100%;
  object-fit: contain;
}

.platform-btn:hover {
  transform: translateY(-1px);
}

.site-footer {
  padding: 56px 18px 28px;
  background: var(--footer);
  color: #fff;
  text-align: center;
}

.footer-brand {
  justify-content: center;
  margin-bottom: 18px;
}

.back-top {
  position: fixed;
  right: 18px;
  bottom: 24px;
  z-index: 40;
  width: 48px;
  height: 48px;
  padding: 0;
  border-radius: 50%;
  background: transparent;
  box-shadow: none;
}

.back-top img {
  display: block;
  width: 100%;
  height: 100%;
  object-fit: contain;
}

.back-top[hidden] {
  display: none;
}

.footer-links {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 10px;
  color: rgba(255, 255, 255, 0.55);
  font-size: 0.82rem;
}

.footer-links a:hover {
  color: #fff;
}

@media (min-width: 768px) {
  .hero,
  .features,
  .sdk,
  .download {
    width: min(100% - 40px, 920px);
    margin-left: auto;
    margin-right: auto;
  }

  .feature-grid {
    gap: 48px 40px;
  }

  .feature-icon {
    width: 140px;
    height: 140px;
    margin-bottom: 18px;
  }

  .feature-card h3 {
    margin-bottom: 10px;
    font-size: 1.1rem;
  }

  .feature-card p {
    font-size: 0.92rem;
    line-height: 1.7;
  }

  .feature-card {
    max-width: none;
  }

  .platform-grid {
    grid-template-columns: repeat(5, minmax(0, 1fr));
    max-width: 760px;
  }

  .platform-card:nth-child(5) {
    grid-column: auto;
    width: auto;
    margin: 0;
  }
}

@media (max-width: 380px) {
  .web-entry {
    padding: 7px 12px;
    font-size: 0.8rem;
  }

  .hero-desc {
    font-size: 0.88rem;
  }
}