col-lg-7 text-center .align-middle">

  <div class="v4-v6-toggle">
    <button id="button-show-v4" onclick="showCodeVersion('v4')" type="button" class="btn  btn-secondary btn-sm active">d3 v4</button>
    <span> | </span>
    <button id="button-show-v6" onclick="showCodeVersion('v6')" type="button" class="btn  btn-secondary btn-sm">d3 v6</button>
  </div>

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<aside style="position: -webkit-sticky; position: sticky; top: 120px">&larr; Edit me! </aside>
<pre clas