svg {
  background: white;
}
.node {
  shape-rendering: crispEdges;
  vector-effect: non-scaling-stroke;
  fill: none;
}
.label {
  pointer-events: none;
  fill: #444;
  text-anchor: middle;
  font-family: sans-serif;
  text-shadow: -1px 0 white, 0 1px white, 1px 0 white, 0 -1px white;
}