body {
  font-family: sans-serif;
  background: #f9f9f9;
}

.node circle {
  fill: #4CAF50;
  stroke: #333;
  stroke-width: 2px;
  cursor: pointer;
}

.node text {
  font-size: 14px;
  fill: #333;
}

.link {
  fill: none;
  stroke: #999;
  stroke-width: 2px;
}