<canvas width="600" height="400">
</canvas>
<script>
let pantalla = document.querySelector('canvas');
let pincel = pantalla.getContext('2d');
pincel.fillStyle="lightgrey"
pincel.fillRect(0,0,600,400);
pincel.fillStyle="green"
pincel.fillRect(0,0,200,400);
pincel.fillStyle="white"
pincel.fillRect(200,0,200,400);
pincel.fillStyle="red"
pincel.fillRect(400,0,200,400);
pincel.fillStyle="brown"
pincel.fillRect(250,150,100,100);
</script>