Requirements to create Adobe AIR application

You can do this by implementing a custom Border:

package your.package
{

  import flash.display.*;
  import flash.geom.*;
  import flash.utils.*;

  import mx.skins.halo.HaloBorder;
  import mx.utils.GraphicsUtil;

  public class RoundedBorder extends HaloBorder 
  {

    private var topCornerRadius:Number;
    private var bottomCornerRadius:Number;
    private var setup:Boolean;

    /**
     * Get the CSS style attributes from the element to which to apply this
     * gradient. 
     */
    private function readElementCssStyles():void
    {
      topCornerRadius = getStyle("cornerRadius") as Number;
      if (!topCornerRadius)
      { 
        topCornerRadius = 0;
      }    

      bottomCornerRadius = getStyle("bottomCornerRadius") as Number;
      if (!bottomCornerRadius) 
      {
        bottomCornerRadius = topCornerRadius;
      }  
    }

    /**
     * Paint the gradient background.
     *  
     * @param unscaledWidth
     * @param unscaledHeight
     * 
     */
    override protected function updateDisplayList(unscaledWidth:Number, unscaledHeight:Number):void
    {
      super.updateDisplayList(unscaledWidth, unscaledHeight);   
      var rectWidth:Number 
          = unscaledWidth - this.borderMetrics.left - this.borderMetrics.right;
      var rectHeight:Number 
          = unscaledHeight - this.borderMetrics.top - this.borderMetrics.bottom; 

      readElementCssStyles();

      var topRadius:Number = Math.max(topCornerRadius-2, 0);
      var bottomRadius:Number = Math.max(bottomCornerRadius-2, 0);

      GraphicsUtil.drawRoundRectComplex(this.graphics, 
                                        this.borderMetrics.left, 
                                        this.borderMetrics.top, 
                                        rectWidth, 
                                        rectHeight, 
                                        topRadius, 
                                        topRadius, 
                                        bottomRadius, 
                                        bottomRadius);
    }

  }
}

Then in your MXML application you have to define a CSS class for your VBox like this:

  <mx:Style>
    .roundedBorder
    {
      border-style:solid;
      border-thickness: 1;
      border-skin: ClassReference("your.package.RoundedBorder");
      corner-radius: 5;
    }   
  </mx:Style>

I have ripped this code out of a more complex class. Hope I did not forgot anything and that it will work as posted.

The ScaleNine themes are a good place to start, find one that is sort of like what you want, plug it into your app, and gradually replace the colors, images, and controls with your own.

http://www.scalenine.com/