      <p style="max-width: 700px; margin: auto">
          This post follows the previous
          <a href="bubble_basic.html">basic bubble plot</a>. It extends it,
          adding the information of a fourth variable mapped to the bubble
          <u>color</u>. Visit the
          <a href="../bubble.html">bubble plot</a> section for more examples.
          This example works with d3.js <code>v4</code> and <code>v6</code>
        </p>
        <br />
        <a class="btn btn-secondary btn-md text-upperca