title: Jquery change textarea styles when user starts fourth line
body: <p>I have a textarea with a background, set by css. I want to remove this when the user has started the 4th line.</p>
  
  <p>HTML</p>
  
  <pre><code>&lt;textarea rows='7' cols='60' style='background(image.png)'&gt;&lt;/textarea&gt;
  </code></pre>
  
  <p>Javascript:</p>
  
  <pre><code> $(textarea).css("background","#fff");
  </code></pre>
  
  <p>I just need a trigger</p>
  
  <p>Thanks</p>