style.css

/*svg {
  font: 12px sans-serif;
}

.axis path,
.axis line {
  fill: none;
  stroke: rgba(0, 0, 0, 0.1);
  shape-rendering: crispEdges;
}

.axisLine {
  fill: none;
  shape-rendering: crispEdges;
  stroke: rgba(0, 0, 0, 0.5);
  stroke-width: 2px;
}

rect.pane {
  cursor: move;
  fill: none;
  pointer-events: all;
}*/

rect {
  fill: transparent;
  shape-rendering: crispEdges;
}

.axis path,
.axis line {
  fill: none;
  stroke: rgba(0, 0, 0, 0.1);
  shape-rendering: crispEdges;
}

.axisLine {
  fill: none;
  shape-rendering: crispEdges;
  stroke: rgba(0, 0, 0, 0.5);
  stroke-width: 2px;
}

.dot {
  fill-opacity: .5;
}

.d3-tip {
  line-height: 1;
  font-weight: bold;
  padding: 12px;
  background: rgba(0, 0, 0, 0.8);
  color: #fff;
  border-radius: 2px;
}

/* Creates a small triangle extender for the tooltip */
.d3-tip:after {
  box-sizing: border-box;
  display: inline;
  font-size: 10px;
  width: 100%;
  line-height: 1;
  color: rgba(0, 0, 0, 0.8);
  content: "\25BC";
  position: absolute;
  text-align: center;
}

/* Style northward tooltips differently */
.d3-tip.n:after {
  margin: -1px 0 0 0;
  top: 100%;
  left: 0;
}