Fireworks

@grid: 30 / 60vmin noclip;
border-radius: 50%;
background: hsl(@y(* -12), 80%, 60%);
background: lch(90, 120, @y(*10deg));
animation: f @once.p(5s, 7.5s) ease infinite;
animation-delay: $s(-90/@I*@i(-1)*@x/@y);
@keyframes f {
  0%, 25%, 80% {opacity: 1; scale: .2}
  25%, 75%, 100% {opacity: 0; scale: @r(2, 3)}
}