JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container"></div>
<div id="tooltip">Tooltip!</div>

CSS

#container {
    width: 500px;
    height: 500px;
    border: solid 1px red;
}

#tooltip {
  position: absolute;
}

JavaScript

var container = document.getElementById('container')
var tooltip = document.getElementById('tooltip')

container.onmousemove = function(event) {
  tooltip.style.left = (event.pageX + 20) + 'px'
  tooltip.style.top = event.pageY + 'px'
}