#loading {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,0.3);
  z-index: 9999;
  justify-content: center;
  align-items: center;
}
#loading .spinner {
  width: 40px;
  height: 40px;
  border: 5px solid #ccc;
  border-top-color: #000;
  border-radius: 50%;
  animation: spin .8s linear infinite;
}
@keyframes spin {
  to { transform: rotate(360deg); }
}