// some sample code
<canvas id="canvas" width="838" height="220"></canvas>

<script>
  var canvasContext = document.getElementById("canvas").getContext("2d");
  canvasContext.fillRect(250, 25, 150, 100);

  canvasContext.beginPath();
  canvasContext.arc(450, 110, 100, Math.PI * 1/2, Math.PI * 3/2);
  canvasContext.lineWidth = 15;
  canvasContext.lineCap = 'round';
  canvasContext.strokeStyle = 'rgba(255, 127, 0, 0.5)';
  canvasContext.stroke();

</script>