title: how to make polymer iron-list keep expanding, instead of scolling
body: <p>I am following the example of <a href="https://elements.polymer-project.org/bower_components/iron-list/demo/collapse.html" rel="nofollow noreferrer">collapsible items of iron-list</a>. However, I have more content under the iron-list, say an iron-menu.</p>
  
  <p>The issue is that the height of the iron-list does not dynamically increase as the user expand the iron-list contents. Instead the iron-list becomes scollable, making it hard to see all the contents. </p>
  
  <p>I would like the iron-list to expand in height, and push down the content (iron-menu) below. Is there a way to do this? Many thanks.</p>
  
  <p>I also tried to set the <code>scroll-target</code>, but it doesn't push the content below down. It overlaps the iron-list content onto the content below, which is not what I want.</p>
  
  <pre><code>&lt;iron-list scroll-target="document" ... &gt;
  </code></pre>