<canvas width="400" height="400"></canvas>
<script>
var tela = document.querySelector('canvas');
var pincel = tela.getContext('2d');
pincel.fillStyle = "blue"
pincel.rect (0, 0, 400, 400)
pincel.fill();
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>
