<!DOCTYPE html>
<html lang="pt-br">
<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>Bandeira do Brasil</title>
</head>
<body>
<canvas width="600" height="400"></canvas>
<script>
let canvas = document.querySelector('canvas');
let context = canvas.getContext('2d');
context.fillStyle = 'green';
context.fillRect(0,0,600,400);
context.fillStyle = 'yellow';
context.beginPath();
context.moveTo(300,50);
context.lineTo(50,200);
context.lineTo(550,200);
context.fill();
context.beginPath();
context.moveTo(300,350);
context.lineTo(50,200);
context.lineTo(550,200);
context.fill();
context.fillStyle="darkblue";
context.beginPath();
context.arc(300, 200, 100, 0, 2*3.14);
context.fill();
</script>
</body>
</html>