title: "Type DataGrid in CSS selector 'DataGrid' must be qualified with a namespace" warning when styling in Flex
body: <p>I am attempting to style the headers in a flex datagrid and I keep getting the warning:</p>
  
  <blockquote>
    <p>Type DataGrid in CSS selector 'DataGrid' must be qualified with a namespace</p>
  </blockquote>
  
  <p>What does this mean? I have gone through a bunch of tutorials and none of them have worked.  It seems like changing a the colors in a datagrid should be relatively simple.</p>
  
  <p>Here is a code sample:</p>
  
  <pre><code>&lt;mx:Style&gt;
      .headerCustomStyle
      {
          fontWeight: "bold";
          textAlign: "center";
          color: #0000FF;
      }
  
      DataGrid {
          alternating-item-colors: #F4FBFF, #FFFFFF;
      }
  &lt;/mx:Style&gt;
  
  &lt;mx:DataGrid draggableColumns="true" width="100%" id="topTracks" headerStyleName="headerCustomStyle" dataProvider="{_trackData.track}" &gt;
      &lt;mx:columns&gt;
          &lt;mx:DataGridColumn id="artistName" dataField="artist.name" headerText="Artist" width="250" /&gt;
          &lt;mx:DataGridColumn id="trackName" dataField="name" headerText="Track" width="250"/&gt;
      &lt;/mx:columns&gt;
  &lt;/mx:DataGrid&gt;
  </code></pre>