._dash-loading-callback {
  margin: auto;
  position: relative;
  border: 4px solid #f3f3f3; /* Light gray */
  border-top: 4px solid #3498db; /* Blue */
  border-radius: 50%;
  width: 40px;
  height: 40px;
  animation: spin 1s linear infinite;
}

@keyframes spin {
  0% {
    transform: rotate(0deg);
  }
  100% {
    transform: rotate(360deg);
  }
}