title: How to "dim" certain area in a webpage
body: <p>I have a page which i need to dim a certain area (div) instead of the entire page. How can I achieve this?</p>
  
  <p>I have googled some answer but all of them is about dimming the whole page. Below is the sample code that I got but it dimmed the entire page.</p>
  
  <pre><code>&lt;div id="dimmer"&gt;&lt;/div&gt; 
  
  #dimmer
  {
      background:#000;
      opacity:0.5;
      position:fixed; /* important to use fixed, not absolute */
      top:0;
      left:0;
      width:100%;
      height:100%;
      display:none;
      z-index:9999; /* may not be necessary */
  }
  </code></pre>