I tried to make a function to set the left and top offset of an HTML element. here is the code I tried:

window.addEventListener("mousemove", (e) => {
  let x = e.clientX;
  let y = e.clientY;
  setLeft("demo", x);
  setTop("demo", y);
});
function setLeft(id, left) {
  document.getElementById(id).style.left = left;
}
function setTop(id, top) {
  document.getElementById(id).style.top = top;
}

the "demo" element is set to position:absolute. code gives no error, but does not work. Why?