.circuit-line {
  position: absolute;
  top: 0;
  width: 2px;
  height: 100%;
  background: rgba(0, 255, 255, 0.15);
  animation: flowLine 4s ease-in-out infinite alternate;
  opacity: 0.6;
  border-radius: 2px;
}

@keyframes flowLine {
  0% { transform: translateY(-30%); opacity: 0.2; }
  100% { transform: translateY(30%); opacity: 0.8; }
}