Dimple.js - how to center align legend and create a box around the elements

Question

Is there a way to center align the legend and draw a box around the legend elements in dimple.js? I am trying to achieve the below. Also I want to reduce space between the legend elements. Currently I am using the following command to render the legend.

var legends = chart.addLegend(30, 270, 700, 20, "left");