:root {
  --blue-50: #eef8fb;
  --blue-75: #f7fcff;
  --blue-100: #dff2ff;
  --blue-120: #e8f7ff;
  --blue-300: #5aa9d8;
  --blue-500: #1f7bb6;
  --blue-600: #0b5f9b;
  --blue-700: #07548c;
  --blue-800: #123c7a;
  --blue-900: #071f4c;
  --green-500: #31b96b;
  --green-700: #2f8f6b;
  --sand-50: #fff8ea;
  --sand-100: #fffdf7;
  --text: #1d2330;
  --muted: #4c6b80;
  --line: rgba(31, 123, 182, 0.18);
  --shadow: 0 24px 70px rgba(7, 70, 120, 0.14);
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  color: var(--text);
  background: var(--blue-50);
  font-family: "PingFang SC", "Microsoft YaHei", Arial, sans-serif;
}

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

.site-header {
  position: sticky;
  top: 0;
  z-index: 10;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
  min-height: 68px;
  padding: 12px clamp(20px, 5vw, 72px);
  border-bottom: 1px solid rgba(255, 255, 255, 0.48);
  background: rgba(247, 252, 255, 0.9);
  backdrop-filter: blur(18px);
}

.brand,
.nav-links,
.hero-stats,
.footer-inner {
  display: flex;
  align-items: center;
}

.brand {
  gap: 10px;
  color: var(--blue-800);
  font-size: 18px;
  font-weight: 900;
  white-space: nowrap;
}

.brand-logo {
  width: 38px;
  height: 38px;
  border-radius: 8px;
  object-fit: cover;
  box-shadow: 0 10px 22px rgba(31, 123, 182, 0.22);
}

.nav-links {
  gap: clamp(16px, 3vw, 34px);
  color: #31566d;
  font-size: 15px;
  font-weight: 800;
}

.nav-links a {
  transition: color 0.18s ease, transform 0.18s ease;
}

.nav-links a:hover {
  color: var(--blue-700);
  transform: translateY(-1px);
}

.hero {
  position: relative;
  display: flex;
  align-items: center;
  min-height: calc(78svh - 68px);
  padding: clamp(42px, 5vw, 62px) clamp(20px, 6vw, 88px);
  overflow: hidden;
  color: #ffffff;
  background:
    linear-gradient(90deg, rgba(7, 31, 76, 0.93) 0%, rgba(11, 95, 155, 0.78) 48%, rgba(11, 95, 155, 0.16) 100%),
    url("./assets/study-uni-bg.jpg") center center / cover no-repeat,
    linear-gradient(135deg, var(--blue-800), var(--blue-500));
}

.hero-overlay {
  position: absolute;
  inset: 0;
  background:
    linear-gradient(180deg, rgba(238, 248, 251, 0.06), rgba(7, 31, 76, 0.2)),
    linear-gradient(0deg, rgba(7, 31, 76, 0.12), transparent 42%);
  pointer-events: none;
}

.hero-shell {
  position: relative;
  z-index: 1;
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(350px, 0.74fr);
  gap: clamp(30px, 5vw, 72px);
  align-items: center;
  width: min(1160px, 100%);
  margin: 0 auto;
}

.hero-shell-simple {
  grid-template-columns: minmax(0, 1fr);
}

.hero-content {
  width: min(1080px, 100%);
}

.eyebrow,
.section-kicker,
.board-label {
  margin: 0 0 14px;
  color: var(--blue-100);
  font-size: 13px;
  font-weight: 900;
  letter-spacing: 0;
}

.hero h1 {
  margin: 0;
  max-width: 1080px;
  font-size: clamp(46px, 6.2vw, 86px);
  line-height: 1.02;
  letter-spacing: 0;
}

.hero h1 span {
  display: block;
  white-space: nowrap;
}

.hero-lead {
  max-width: 650px;
  margin: 24px 0 0;
  color: rgba(247, 252, 255, 0.94);
  font-size: clamp(18px, 2.2vw, 24px);
  font-weight: 750;
  line-height: 1.68;
}

.hero-lead span {
  display: block;
}

.download-actions {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 12px;
  width: min(560px, 100%);
  margin-top: 28px;
}

.download-button {
  display: grid;
  grid-template-columns: 42px minmax(0, 1fr);
  gap: 12px;
  align-items: center;
  min-height: 66px;
  padding: 12px 14px;
  border: 1px solid rgba(255, 255, 255, 0.52);
  border-radius: 8px;
  color: var(--blue-900);
  background: rgba(255, 255, 255, 0.94);
  box-shadow: 0 14px 32px rgba(7, 31, 76, 0.18);
  transition: transform 0.18s ease, box-shadow 0.18s ease, background 0.18s ease;
}

.download-button:hover {
  transform: translateY(-2px);
  background: #ffffff;
  box-shadow: 0 18px 42px rgba(7, 31, 76, 0.24);
}

.download-button strong,
.download-button small {
  display: block;
}

.download-button strong {
  font-size: 15px;
  line-height: 1.2;
}

.download-button small {
  margin-top: 4px;
  color: #55758a;
  font-size: 12px;
  font-weight: 800;
  line-height: 1.25;
}

.download-icon,
.method-icon,
.feature-icon {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 42px;
  height: 42px;
  border-radius: 8px;
  color: #ffffff;
  font-size: 17px;
  font-weight: 900;
}

.download-button-android .download-icon {
  background: linear-gradient(135deg, var(--green-500), var(--green-700));
}

.download-button-mac .download-icon {
  background: linear-gradient(135deg, var(--blue-300), var(--blue-700));
}

.hero-stats {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 12px;
  width: min(560px, 100%);
  margin: 26px 0 0;
  padding: 0;
}

.hero-stats div {
  min-width: 0;
  padding: 14px 16px;
  border: 1px solid rgba(223, 242, 255, 0.26);
  border-radius: 8px;
  background: rgba(247, 252, 255, 0.13);
  backdrop-filter: blur(10px);
}

.hero-stats dt {
  font-size: 22px;
  font-weight: 900;
}

.hero-stats dd {
  margin: 5px 0 0;
  color: rgba(247, 252, 255, 0.76);
  font-size: 13px;
  font-weight: 750;
}

.learning-flow {
  display: grid;
  grid-template-columns: minmax(240px, 0.64fr) minmax(0, 1fr);
  gap: 24px;
  align-items: center;
  margin-bottom: 18px;
  padding: 22px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: rgba(255, 255, 255, 0.82);
  box-shadow: 0 14px 36px rgba(7, 70, 120, 0.08);
  color: var(--text);
}

.plan-header {
  padding: 4px;
}

.plan-header .board-label {
  color: var(--blue-700);
}

.plan-header strong {
  display: block;
  color: var(--blue-900);
  font-size: clamp(24px, 3vw, 34px);
  line-height: 1.15;
}

.plan-list {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 10px;
  margin: 0;
  padding: 0;
  list-style: none;
}

.plan-list li {
  display: grid;
  grid-template-columns: 36px minmax(0, 1fr);
  gap: 12px;
  padding: 14px;
  border: 1px solid rgba(31, 123, 182, 0.12);
  border-radius: 8px;
  background: rgba(255, 255, 255, 0.78);
}

.plan-list span {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 32px;
  height: 32px;
  border-radius: 8px;
  color: #ffffff;
  background: var(--blue-500);
  font-size: 12px;
  font-weight: 900;
}

.plan-list strong {
  color: var(--blue-800);
  font-size: 17px;
}

.plan-list p {
  margin: 5px 0 0;
  color: var(--muted);
  font-size: 14px;
  font-weight: 700;
  line-height: 1.55;
}

.section {
  padding: clamp(72px, 9vw, 118px) clamp(20px, 6vw, 88px);
}

.section-inner,
.download-band-inner {
  width: min(1160px, 100%);
  margin: 0 auto;
}

.section-heading {
  max-width: 780px;
  margin-bottom: clamp(30px, 5vw, 52px);
}

.section-kicker {
  display: inline-flex;
  align-items: center;
  min-height: 30px;
  padding: 0 12px;
  border-radius: 8px;
  color: var(--blue-700);
  background: var(--blue-100);
}

.section h2,
.download-band h2 {
  margin: 0;
  color: var(--blue-900);
  font-size: clamp(31px, 5vw, 52px);
  line-height: 1.14;
  letter-spacing: 0;
}

.method-section {
  background: linear-gradient(180deg, var(--blue-75), var(--blue-50));
}

.method-grid,
.feature-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 18px;
}

.method-card,
.feature-card,
.system-cards article {
  min-height: 100%;
  padding: 26px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: rgba(255, 255, 255, 0.86);
  box-shadow: 0 14px 36px rgba(7, 70, 120, 0.08);
}

.method-icon,
.feature-icon {
  background: linear-gradient(135deg, var(--blue-500), var(--green-500));
}

.method-card h3,
.feature-card h3,
.system-cards strong {
  display: block;
  margin: 16px 0 10px;
  color: var(--blue-800);
  font-size: 22px;
  line-height: 1.25;
}

.method-card p,
.feature-card p,
.system-copy p,
.system-cards p {
  margin: 0;
  color: var(--muted);
  font-size: 16px;
  font-weight: 650;
  line-height: 1.78;
}

.system-section {
  background:
    linear-gradient(90deg, rgba(255, 248, 234, 0.72), rgba(223, 242, 255, 0.74)),
    var(--sand-100);
}

.system-layout {
  display: grid;
  grid-template-columns: minmax(0, 0.95fr) minmax(320px, 1fr);
  gap: clamp(32px, 6vw, 78px);
  align-items: center;
}

.system-copy p {
  max-width: 630px;
  margin-top: 22px;
  font-size: 18px;
}

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

.system-cards span {
  display: inline-flex;
  min-height: 30px;
  align-items: center;
  padding: 0 12px;
  border-radius: 8px;
  color: var(--blue-700);
  background: var(--blue-100);
  font-size: 13px;
  font-weight: 900;
}

.features-section {
  background: linear-gradient(180deg, var(--blue-75), var(--blue-120));
}

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

.download-band {
  padding: clamp(58px, 8vw, 86px) clamp(20px, 6vw, 88px);
  color: #ffffff;
  background: linear-gradient(135deg, var(--blue-800), var(--blue-500) 58%, var(--green-700));
}

.download-band-inner {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(360px, 0.75fr);
  gap: 28px;
  align-items: center;
}

.download-band .section-kicker {
  color: var(--blue-900);
  background: rgba(255, 255, 255, 0.9);
}

.download-band h2 {
  color: #ffffff;
}

.download-actions-dark {
  width: 100%;
  margin-top: 0;
}

.site-footer {
  padding: 28px clamp(20px, 6vw, 88px);
  color: rgba(247, 252, 255, 0.76);
  background: var(--blue-900);
}

.footer-inner {
  justify-content: space-between;
  gap: 18px;
  width: min(1160px, 100%);
  margin: 0 auto;
}

.footer-inner strong {
  color: #ffffff;
}

.beian-link {
  color: rgba(247, 252, 255, 0.76);
  font-size: 13px;
  font-weight: 700;
  white-space: nowrap;
  transition: color 0.18s ease;
}

.beian-link:hover {
  color: #ffffff;
}

@media (max-width: 980px) {
  .hero-shell,
  .learning-flow,
  .system-layout,
  .download-band-inner {
    grid-template-columns: 1fr;
  }

  .hero {
    min-height: auto;
    background:
      linear-gradient(180deg, rgba(7, 31, 76, 0.92) 0%, rgba(11, 95, 155, 0.78) 62%, rgba(11, 95, 155, 0.36) 100%),
      url("./assets/study-uni-bg.jpg") center center / cover no-repeat,
      linear-gradient(135deg, var(--blue-800), var(--blue-500));
  }

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

@media (max-width: 720px) {
  .site-header {
    align-items: flex-start;
    flex-wrap: wrap;
    padding: 10px 16px;
  }

  .nav-links {
    order: 3;
    width: 100%;
    gap: 16px;
    overflow-x: auto;
    padding-bottom: 2px;
    font-size: 14px;
  }

  .hero {
    align-items: flex-start;
    padding: 42px 18px 46px;
  }

  .hero-lead {
    font-size: 18px;
  }

  .hero h1 {
    font-size: clamp(38px, 10.4vw, 46px);
  }

  .hero h1 span {
    white-space: normal;
  }

  .download-actions,
  .method-grid,
  .feature-grid {
    grid-template-columns: 1fr;
  }

  .hero-stats {
    gap: 8px;
  }

  .hero-stats div {
    padding: 11px 10px;
  }

  .hero-stats dt {
    font-size: 18px;
  }

  .hero-stats dd {
    font-size: 12px;
  }

  .learning-flow,
  .method-card,
  .feature-card,
  .system-cards article {
    padding: 20px;
  }

  .section {
    padding: 62px 18px;
  }

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

  .download-band {
    padding: 56px 18px;
  }

  .footer-inner {
    align-items: flex-start;
    flex-direction: column;
  }
}