<canvas width="600" height="400"></canvas>
<script>
var tela = document.querySelector('canvas')
var pincel = tela.getContext('2d')
pincel.fillStyle = 'lightgrey';
pincel.fillRect(0, 0, 600, 400);
pincel.fillStyle = 'red'
pincel.fillRect(240, 0, 110, 400);
pincel.fillRect(0, 155, 600, 110);
</script>