codigo
<canvas width="400" height="400"></canvas>
<script type="text/javascript">
var pantalla = document.querySelector("canvas")
var pincel = pantalla.getContext("2d")
pincel.fillStyle = "lightgrey"
pincel.fillRect(0,0,400,400)
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>
