Content does not flash more than 3 times per second

Content that flashes more than three times per second can induce photosensitive seizures in users with photosensitive epilepsy — an estimated 3 in 100,000 people worldwide, with real documented harm. WCAG 2.2 SC 2.3.1 (Three Flashes or Below Threshold) is a Level A requirement. This is not a theoretical risk: the Pokémon seizure incident in 1997 caused over 600 hospitalizations. Strobe-effect loading animations and attention-seeking flashing banners are the most common sources.

Replace any high-frequency flashing animation with a smooth, low-frequency alternative that pulses rather than flickers.

/* Bad — flashes at ~2Hz (above the danger threshold on short loops) */
@keyframes flash {
  0%, 49% { opacity: 1; background: white; }
  50%, 100% { opacity: 1; background: black; }
}
.bad-loader { animation: flash 0.3s infinite; } /* 3.3 Hz — dangerous */

/* Good — gentle fade at 0.5 Hz, well below the 3Hz threshold */
@keyframes pulse {
  0%, 100% { opacity: 0.6; }
  50% { opacity: 1; }
}
.loader { animation: pulse 2s ease-in-out infinite; }

Also apply @media (prefers-reduced-motion: reduce) { .loader { animation: none; } } to disable all motion for users who have requested it in their OS settings.