title: Change default css in extjs 4.2.1 CSS Variables
body: <p>everybody I am new in extjs. I am using extjs 4.2.1. and there is one new tab "CSS Vars" in ExtJS docs. but I can't set that variables config in normal way. Can anyone suggest me how to change default CSS behavior of extjs (4.2.1) using CSS vars ?</p>
  
  <p>for example I want to set back-ground color of panel using $panel-body-background-color. then
  how can I set in panel config ? I am getting error in following peace of code.</p>
  
  <pre><code>xtype:'panel',
  border:true,
  $panel-body-background-color : 'black'
  </code></pre>