sombra de caja d3
/* For the drop shadow filter... */
var defs = svg.append("defs");
var filter = defs.append("filter")
.attr("id", "dropshadow")
filter.append("feGaussianBlur")
.attr("in", "SourceAlpha")
.attr("stdDeviation", 4)
.attr("result", "blur");
filter.append("feOffset")
.attr("in", "blur")
.attr("dx", 2)
.attr("dy", 2)
.attr("result", "offsetBlur");
var feMerge = filter.append("feMerge");
feMerge.append("feMergeNode")
.attr("in", "offsetBlur")
feMerge.append("feMergeNode")
.attr("in", "SourceGraphic");
McShanmukh