<i style="--x:300px;--y:100px;"></i>

<button> Run the animation </button>
i{
  position:fixed;
  width:50px;
  height:50px;
  border-radius:50%;
  background:radial-gradient(at 30% 30%,#0000,#000a) red;
  left:var(--x);
  top: var(--y);
}
i.start {
  animation: x 1s, y 0.5s;
  animation-timing-function:cubic-bezier(.5,-800,.5,800);
  animation-iteration-count:infinite;
}
@keyframes x { to { left:calc(var(--x) + 1px); } }
@keyframes y { to { top :calc(var(--y) + 0.2px); } }


/**/
d {position:fixed;height:4px;width:4px;background:#222;border-radius:50%}
button {border:none;border-radius:10px;padding:10px 20px;cursor:pointer;position:fixed;top:20px;right:20px;font-family:sans-serif;font-size:30px;background:#c82629;color:#fff;}
let elem = document.querySelector('i');
let start;

function debug(timestamp) {
  if (start === undefined)
    start = timestamp;
  const elapsed = timestamp - start;
  let rect = elem.getBoundingClientRect();
  document.body.insertAdjacentHTML("beforeBegin",'<d style="top:'+(rect.y + rect.height/2)+'px;left:'+(rect.x + rect.width/2)+'px;"></d>')

  if (elapsed < 3000) { 
    window.requestAnimationFrame(debug);
  }
}


document.querySelector("button").addEventListener("click",function() {
  elem.classList.add("start");
  window.requestAnimationFrame(debug);
})

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