<section class="tickets" id="tickets">
  <div class="align-center">
    <h3>Buy tickets</h3>

    <p>
      Your ticket includes access to all sessions, breakfast, lunch and free
      drinks.<br />

      <b>Please note:</b> You have the opportunity to purchase early bird
      tickets at a discounted price until October 15th.<br />

      <b>Book your tickets now!</b>
    </p>

    <div style="width:95%; margin: 0 auto;" ><iframe id="eb" name="eb" src="https://eventbrite.com/tickets-external?eid=27090343948&ref=etckt" frameborder="0" height="320" width="100%" vspace="0" hspace="0" marginheight="5" marginwidth="5" scrolling="auto"></iframe><div style="font-family:Helvetica, Arial; font-size:10px; padding:5px 0 5px; margin:2px; width:100%; text-align:left;" ><a class="powered-by-eb" style="color: #dddddd; text-decoration: none;" target="_blank" href="http://www.eventbrite.com/l/registration-online/">Powered by Eventbrite</a></div></div>

  </div>
</section>

<section class="tickets" id="tickets">
  <div class="align-center">
    <h3>Buy tickets</h3>

    <p>
      Your ticket includes access to all sessions, breakfast, lunch and free
      drinks.<br />

      <b>Please note:</b> You have the opportunity to purchase early bird
      tickets at a discounted price until October 15th.<br />

      <b>Book your tickets now!</b>
    </p>

    <div style="width:95%; margin: 0 auto;" ><iframe id="eb" name="eb" src="https://eventbrite.com/tickets-external?eid=27090343948&ref=etckt" frameborder="0" height="400" width="100%" vspace="0" hspace="0" marginheight="5" marginwidth="5" scrolling="auto"></iframe><div style="font-family:Helvetica, Arial; font-size:10px; padding:5px 0 5px; margin:2px; width:100%; text-align:left;" ><a class="powered-by-eb" style="color: #dddddd; text-decoration: none;" target="_blank" href="http://www.eventbrite.com/l/registration-online/">Powered by Eventbrite</a></div></div>

  </div>
</section>

Fix the eventbrite the height.
Fix the eventbrite the height.