#spotlight{position:fixed;inset:0;z-index:4;pointer-events:none;opacity:0;
  transition:opacity .5s ease;mix-blend-mode:screen;
  background:radial-gradient(560px circle at var(--sx,50%) var(--sy,50%), rgba(139,108,255,.16), transparent 70%)}
#spotlight.on{opacity:1}
@media(pointer:coarse),(prefers-reduced-motion:reduce){#spotlight{display:none}}