JSFiddle - React, Tailwind, and code Playground

HTML

<div id="test"></div>
<div id="out">bla</div>

CSS

#test{
    width:40px;
    height:40px;
    background-color:#000;
    position:absolute;
}

JavaScript

var div = document.getElementById('test');
var out = document.getElementById('out');
var mouseDown = false;
window.onmousemove = function(e){
    if(mouseDown == true){
    out.innerHtml = parseInt(div.style.top, 10);
    div.style.top = (e.pageY-parseInt(div.style.top, 10))+'px';
    div.style.left = (e.pageX-parseInt(div.style.left, 10))+'px';
    }
};
div.onmousedown = function(){
	mouseDown = true;
};
window.onmouseup = function(){
	mouseDown = false;
};