superset/caravel/assets/visualizations/sankey.css

.sankey .node rect {
  cursor: move;
  fill-opacity: .9;
  shape-rendering: crispEdges;
}

.sankey .node text {
  pointer-events: none;
  text-shadow: 0 1px 0 #fff;
}

.sankey .link {
  fill: none;
  stroke: #000;
  stroke-opacity: .2;
}

.sankey .link:hover {
  stroke-opacity: .5;
}

.sankey-tooltip {
  position: absolute;
  width: auto;
  background: #ddd;
  padding: 10px;
  font-size: 12px;
  font-weight: 200;
  color: #333;
  border: 1px solid #fff;
  text-align: center;
  pointer-events: none;
}