Контур и граница в Fabricjs

var canvas = this.__canvas = new fabric.StaticCanvas('c');

var rectBack = new fabric.Rect({
  width: 170,
  height: 170,
  top: 0,
  left: 0,
  fill: 'rgba(0,0,255,1.0)',
  rx: 2,
  ry: 2
});

var outerMargin = 10
var innerOutlineWidth = 4

var innerOutline = new fabric.Rect({
  width: 170 - outerMargin - innerOutlineWidth/2,
  height: 170 - outerMargin - innerOutlineWidth/2,
  top: outerMargin/2,
  left: outerMargin/2,
  stroke: 'rgba(255,255,255,1.0)',
  fill: 'rgba(0,0,0,0.0)',
  strokeWidth: innerOutlineWidth,
  rx: 10,
  ry: 10
});

var group = new fabric.Group([rectBack, innerOutline], {
  left: 0,
  top: 0,
  angle: 0
});

canvas.add(group);

<script src = "https://cdnjs.cloudflare.com/ajax/libs/fabric.js/2.7.0/fabric.min.js"></script>
<canvas id = "c" width = "200" height = "200"></canvas>