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

/* Para compatibilidade com navegadores mais antigos (opcional mas recomendado) */
@-webkit-keyframes spin {
  0% { -webkit-transform: rotate(0deg); }
  100% { -webkit-transform: rotate(360deg); }
}

#loading {
    display: block;
    position: fixed;
    left: 50%;
    top: 50%;
    transform: translate(-50%, -50%);
    border: 16px solid #f3f3f3;
    border-radius: 50%;
    border-top: 16px solid #000000;
    width: 30px;
    height: 30px;
    -webkit-animation: spin 2s linear infinite;
    animation: spin 2s linear infinite;
    animation-direction: reverse;
    z-index: 20;
}