JSFiddle - React, Tailwind, and code Playground

HTML

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
<script language="javascript">
function main(){
    var canvas = document.getElementById("canvas");
    canvas.addEventListener("mousemove", function(e){
        if (!e) e = window.event;
        var ctx = canvas.getContext("2d");

        var x = e.offsetX==undefined?e.layerX:e.offsetX;
        var y = e.offsetY==undefined?e.layerY:e.offsetY;

        ctx.fillRect(x, y, 1, 1);
    });
}
</script>
</head>
<body onload="main();">
<div style="width: 800px; height: 600px; -webkit-transform: scale(0.75,0.75); -moz-transform: scale(0.75,0.75)">
    <canvas id="canvas" width="400px" height="400px" style="background-color: #cccccc;border:none"></canvas>
</div>
</body>
</html>