<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
</head>
<body>
<canvas width="600" height="500"></canvas>
</body>
<script>
var pantalla=document.querySelector("canvas");
var pincel=pantalla.getContext("2d")
pincel.fillStyle="black"
pincel.beginPath();
pincel.moveTo(50,50)
pincel.lineTo(50,400)
pincel.lineTo(400,400)
pincel.fill();
pincel.fillStyle="white"
pincel.beginPath();
pincel.moveTo(100,175)
pincel.lineTo(100,350)
pincel.lineTo(275,350)
pincel.fill();
</script>
</html>