title: How to get element's attribute set in CSS class
body: <p>I want to read the element's height and width.</p>
  
  <pre><code>&lt;style type="text/css"&gt;
      .big {
          height: 100px;
          width: 100px
      }
  &lt;/style&gt;
  
  &lt;div id="box1" style="width:50px; height=50px;"&gt;&lt;/div&gt;
  &lt;div id="box2" class="big"&gt;&lt;/div&gt;
  </code></pre>
  
  <p>For <code>box01</code> I can use <code>height=getElementById("box01").style.height</code> - that's fine.</p>
  
  <p>But for box02 it doesn't work. It returns nothing.</p>