LineChart2-highlight.css

.line-chart .highlight-mark {
  fill: #FA7F9F;
  stroke: #891836;
  stroke-width: 1px;
}

LineChart2-render.js

  render() {
    const { data, width, height, xKey, yKey, highlight } = this.props;
    const { x, y, line } = this._chartComponents();

    let highlightMark;
    if (highlight) {
      highlightMark = <circle cx={x(highlight[xKey])} cy={y(highlight[yKey])} r={4} 
                              className='highlight-mark' />;
    }

    return (
      <div>
        <svg ref='svg' width={width} height={height} className='chart line-chart'>
          <path d={line(data)} className='series' />
          {highlightMark}
        </svg>
      </div>
    );
  }