I had to access the jit.js library and under the sunburst 'multipie' config, ie:
'multipie': {
'render': function(node, canvas) {
var height = node.getData('height');
var ldist = height? height : this.config.levelDistance;
var span = node.getData('span') / 2, theta = node.pos.theta;
var begin = theta - span, end = theta + span;
var polarNode = node.pos.getp(true);
var polar = new Polar(begin, polarNode.rho);
var p1coord = polar.getc(true);
polar.theta = end;
var p2coord = polar.getc(true);
polar.rho += ldist;
var p3coord = polar.getc(true);
polar.theta = begin;
var p4coord = polar.getc(true);
var ctx = canvas.getCtx();
ctx.moveTo(0, 0);
ctx.beginPath();
ctx.arc(0, 0, polarNode.rho, begin, end, false);
ctx.arc(0, 0, polarNode.rho + ldist, end, begin, true);
ctx.moveTo(p1coord.x, p1coord.y);
ctx.lineTo(p4coord.x, p4coord.y);
ctx.moveTo(p2coord.x, p2coord.y);
ctx.lineTo(p3coord.x, p3coord.y);
ctx.fill();
I added the following:
ctx.strokeStyle = "rgba(247, 247, 247, 0.96)";
ctx.lineWidth = 0.5;
ctx.save();
ctx.clip();
ctx.lineWidth *= 2;
ctx.fill();
ctx.stroke();
ctx.restore();
The width and color of the stroke is set by ctx.lineWidth and ctx.strokeStyle
Can someone suggest a way of doing this without accessing the library?