@media (max-width: 768px) {
  nav { padding: 0 20px; }
  .hero { padding: 100px 20px 60px; }
  .card-grid { grid-template-columns: 1fr; }
  .hero-cta { flex-direction: column; width: 100%; }
  .hero-cta .btn-primary,
  .hero-cta .btn-secondary { width: 100%; justify-content: center; }

  /* 核心概念三循环：移动端纵向 */
  .cycle-flow { flex-direction: column; }
  .cycle-connector { display: none; }

  /* 响应式几何元素 — 减少数量、缩小尺寸 */
  .geo-hex-2, .geo-hex-3 { display: none; }
  .geo-tri-2 { display: none; }
  .geo-ring-2 { display: none; }
  .geo-hex-1 { width: 50px; height: 58px; top: 12%; left: 4%; }
  .geo-tri-1 { width: 60px; height: 52px; }
  .geo-ring-1 { width: 180px; height: 180px; }
}