.spinner {
  width: 20px;
  height: 20px;
  border: 3px solid #fff;
  border-top: 3px solid transparent;
  border-radius: 50%;
  animation: spin 1s linear infinite;
  margin: auto;
}

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