button.is-submitting, input.is-submitting { cursor: progress; }
button.is-submitting::after {
  content: ""; display: inline-block; width: .85em; height: .85em;
  margin-inline-start: .5em; vertical-align: middle; border: 2px solid currentColor;
  border-inline-end-color: transparent; border-radius: 50%;
  animation: submit-spin .8s linear infinite;
}
@keyframes submit-spin { to { transform: rotate(360deg); } }
@media (prefers-reduced-motion: reduce) { button.is-submitting::after { animation: none; } }