<canvas width="600" heitght="400"></canvas>

<script>

    var tela = document.querySelector("canvas");
    var pincel = tela.getContext("2d");

    pincel.fillStyle = "lightgrey";
    pincel.fillRect(0, 0, 600, 400);

    pincel.fillStyle = "green";
    pincel.fillRect(0, 0, 200, 400);

    pincel.fillStyle = "red";
    pincel.fillRect(400, 0, 200, 400);

    pincel.fillStyle = "yellow";
    pincel.beginPath();
    pincel.moveTo(300, 200);
    pincel.lineTo(200, 400);
    pincel.lineTo(400, 400);
    pincel.fill();


    pincel.fillStyle = "blue";
        pincel.beginPath();
        pincel.arc(300, 200, 50, 0, 2 * 3.14);
        pincel.fill();



</script>