title: height of <div> tag
body: <p>I have 2 divs in my page: <code>&lt;div id="firtdiv" style="top:100px; left:200px; height:unknown"&gt;&lt;/div&gt; &lt;div style="top:unknow; height:200px" id="seconddiv"&gt;&lt;/div&gt;</code></p>
  
  <p>I will set firstdiv's height auto because I will put a datalist so I don't know it's height.
  And secondiv's top property will change according to the fistdiv's height. Second div is bottom of firstdiv.</p>
  
  <p>How can I do?</p>