svg {
  background: white;
}
.node {
  shape-rendering: crispEdges;
  vector-effect: non-scaling-stroke;
  fill: none;
}
.label {
  text-anchor: middle;
  font-family: sans-serif;
  /*text-shadow: -1px 0 white, 0 1px white, 1px 0 white, 0 -1px white;*/
  text-shadow: -2px 0 white, 0 2px white, 2px 0 white, 0 -2px white, -1px -1px white, 1px -1px white, 1px 1px white, -1px 1px white;
}