index.css

/* CSS based on based on https://bl.ocks.org/alandunning/4c36eb1abdb248de34c64f5672afd857 by Alan Dunning. I created my own version of it and added some code */

body {
  background-color: #F1F3F3;
  font-family: 'Questrial', sans-serif;
}

h1 {
  padding-left: 370px;
}

select {
  width: 150px;
  height: 20px;
  font-size: 1em;
  margin: 1em;
}

.axis {
	font: 15px sans-serif;
}

.axis path,
.axis line {
  fill: none;
  stroke: #D4D8DA;
  stroke-width: 2px;
  shape-rendering: crispEdges;
}

#chart {
	position: absolute;
	top: 50px;
	left: 100px;
}

circle {
  cursor: pointer;
}
  .toolTip {
  pointer-events: none;
	position: absolute;
    display: none;
  min-width: 50px;
  height: auto;
  background: none repeat scroll 0 0 #ffffff;
  padding: 9px 14px 6px 14px;
  border-radius: 2px;
  text-align: center;
  line-height: 1.3;
  color: #5B6770;
  box-shadow: 0px 3px 9px rgba(0, 0, 0, .15);
}

.toolTip:after {
  content: "";
  width: 0;
  height: 0;
  border-left: 12px solid transparent;
  border-right: 12px solid transparent;
  border-top: 12px solid white;
  position: absolute;
  bottom: -10px;
  left: 50%;
  margin-left: -12px;
}

.toolTip span {
	font-weight: 500;
  color: #081F2C;
}