.spinner {
  width: 400px;
  height: 400px;
  border: 15px solid rgba(0, 0, 0, 0.1);
  border-left-color: #000;
  border-radius: 50%;
  animation: spin 1s linear infinite;
  margin: 20px auto; /* center on page */
}

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