body, svg {
  font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
  width: 960px;
  height: 500px;
  position: relative;
}

circle, rect {
  stroke: black;
  stroke-width: 2px;
  fill: 'blue';
  fill-opacity: 0.1;
}

.tooltip {
    margin: 30px 30px 30px 30px;
    background-color: lightgray;
    border-style: solid;
    padding: 10px 10px 10px 10px;
    font-size: 1.5em;
    position: absolute;
    z-index: 100;
}