SOURCE

var canvas = document.getElementById("canvas");
if (canvas.getContext) {
  var ctx = canvas.getContext("2d");

  ctx.fillStyle = "rgb(200,0,0)";
  ctx.fillRect(10, 10, 55, 50);

  ctx.fillStyle = "rgba(0, 0, 200, 0.5)";
  ctx.fillRect(30, 30, 55, 50);
}

<canvas id="tutorial" width="150,height=150">
</canvas>