MultiLine circles

HTML

<script src="//d3js.org/d3.v3.min.js"></script>
<div id="chart">
</div>

CSS

.axis path,
      .axis line {
        fill: none;
        stroke: #000;
        shape-rendering: crispEdges;
      }

      text {
        font-size: 75%;
      }

      .line {
        fill: none;
        stroke-width: 1.5px;
      }

      div.tooltipDetail {
        position: absolute;
        height: 50px;
        padding: 4px;
        font-size: 11px;
        background: rgba(192, 192, 192, 0.6);
        pointer-events: none;
        border-radius: 5px;
      }

      div.tooltipSummary {
        position: absolute;
        height: 20px;
        padding: 4px;
        font-size: 11px;
        background: rgba(192, 192, 192, 0.6);
        pointer-events: none;
        border-radius: 5px;
      }

JavaScript

var data =...