style.css

.svg-container {
    display: inline-block;
    position: relative;
    width: 100%;
    padding-bottom: 60%; /* aspect ratio */
    vertical-align: top;
    overflow: hidden;
}
.svg-content-responsive {
    display: inline-block;
    position: absolute;
    top: 10px;
    left: 0;
    background: rgb(.1, .1, .1);
}

.nodes {
  stroke: #fff;
  stroke-width: 1.5px;
}

.links {
  stroke: #999;
  stroke-opacity: .6;
}

.d3-tip {
  line-height: 1;
  font-weight: bold;
  padding: 12px;
  background: rgba(0, 0, 0, 0.5);
  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;
}