[bes]

так пойдёт?

<style>
	div {
		position: absolute;
		left: 40%;
		top: 40%;
		width: 50px;
		height: 50px;
		background: lightgreen;
		padding: 20px;
	}
</style>


<div>div</div><span></span>

<script>
window.onload = function () {

	document.body.children[0].onmousemove = function (e) {
		e = e || event;
		var coords = this.getBoundingClientRect();
		var x = parseInt(e.clientX - coords.left);
		var y = parseInt(e.clientY - coords.top);
		this.nextSibling.innerHTML = x + '<br>' + y;
	}
}
</script>