.loading {
  display: block;
  width: 24px;
  height: 24px;
  border: 3px solid rgba(255,255,255,.3);
  border-radius: 50%;
  border-top-color: #000;
  animation: spin 1s ease-in-out infinite;
}

@keyframes spin {
  to { transform: rotate(360deg); }
}