title: how to set child div width 80% to parent div
body: <p>i want to set child div width to be 80% of parent div. how to do</p>
  
  <pre><code>&lt;div id='container'&gt;
  
          &lt;div id="toolbar" class="ui-widget-header ui-corner-all" style="padding:3px; vertical-align: middle; white-space:nowrap; overflow: hidden;"&gt;
              &lt;button id="BtnPreviousMonth"&gt;Previous Month&lt;/button&gt;
              &lt;button id="BtnNextMonth"&gt;Next Month&lt;/button&gt;
          &lt;/div&gt;
  
          &lt;div id='subcontainer'&gt;
  
          &lt;div id="mycal" style="position:absolute;"&gt;&lt;/div&gt;
  &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>when i set mycal width and height in %. it has no effect. any suggestions ?</p>