JSFiddle - React, Tailwind, and code Playground

HTML

<body>
  <div id="wrapper" onmousemove="coords(event)" onmouseout="clear_coords()">
  <p id="disp"></p>
</div><!--/#wrapper-->

<script>
function coords(test) {
	//coordinates of mouse pointer relative to window size in pixels
	var x = test.clientX;
	var y = test.clientY;
			
	document.getElementById("disp").innerHTML = "Coordinates relative to viewport<br>X coords: " + x + "<br>Y coords: " + y;

}

function clear_coords() {
	var win_width = document.getElementById("wrapper").offsetWidth;
	var win_height = document.getElementById("wrapper").offsetHeight;
	document.getElementById("disp").innerHTML = "X coords: 0<br>Y coords: 0";
}
</script>

CSS

html, body {
  width: 100%;
  height: 100%;
  padding: 0;
  margin: 0;
}

body {
  background-color: rgba(100,100,100,0.2);
  overflow: hidden;
}

#wrapper {
  width: 100%;
  min-height: 100%;
  margin: 0 auto;
  position: relative;
}