JSFiddle - React, Tailwind, and code Playground

HTML

<div id="camada" style="border:solid 1px #F00; position:absolute; top:10px; width:500px; height:200px; left:50px;">
    <p style="border:solid 1px #090; position:absolute; top:5px; left:100px">Paragraph</p>
</div>
<span id="y" style="color:#009;">0</span>

JavaScript

var doc = document.getElementById('camada');
var y = document.getElementById('y');

doc.onmousemove = function(evt) {
    var cursPositionY = evt.layerY ? evt.layerY : window.event.offsetY;
	y.textContent = cursPositionY;
};