@anirudhspriyan,
Are you looking to add border radius to chart container? If yes, you can add it through CSS as shown in the code-snippet below.
.canvasjs-chart-canvas {
border-radius: 12px;
}
#chartContainer {
border: 1px solid #dedede;
border-radius: 12px;
}
Also, check out this JSFiddle for complete working code.

—-
Manoj Mohan
Team CanvasJS