html, body {
  margin: 0;
  height: 100%;
  background: #000;
}

.strobe {
  min-height: 100vh;
  min-height: 100dvh;
  cursor: none;
  /* ~10 flashes per second: a short white hit, then black */
  animation: flash 100ms steps(1, end) infinite;
}

@keyframes flash {
  0% { background: #fff; }
  30% { background: #000; }
}

/* People who asked their OS for reduced motion get a dark screen instead of flashes. */
@media (prefers-reduced-motion: reduce) {
  .strobe { animation: none; }
}