Bandeira Brasil

<meta charset="utf-8">

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

<script>

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

    //verde
        pincel.fillStyle = 'green'
        pincel.fillRect(0, 0, 600, 400);

    //amarelos
        pincel.fillStyle = 'yellow'
        pincel.beginPath ();
            pincel.moveTo (300, 50);
            pincel.lineTo (50, 200);
            pincel.lineTo (400, 200);
            pincel.lineTo (550, 200);
        pincel.fill();

        pincel.beginPath ();
            pincel.moveTo (300, 350);
            pincel.lineTo (50, 200);
            pincel.lineTo (400, 200);
            pincel.lineTo (550, 200);
        pincel.fill();

    //arco
        pincel.fillStyle = 'darkblue'
        pincel.beginPath ();
            pincel.arc (300, 200, 100, 0, 2*3.14);
        pincel.fill();

</script>