Create a CSS file to use these skin classes, and add the CSS to the main project file index.mxml

Create a CSS file, such as custom_css.css:

/* CSS file */ 
@namespace s "library://ns.adobe.com/flex/spark"; 
@namespace mx "library://ns.adobe.com/flex/mx"; 
@namespace custom "com.adobe.customizations.*"; 
@namespace presentation "com.adobe.solutions.cmg.manage.presentation.*"; 
 
presentation|AssetEditorsStack 
{ 
                skinClass : ClassReference("com.adobe.customizations.ExtendedAssetEditorStackSkin"); 
} 
 
custom|ExtendedLetterEditor 
{ 
                skinClass : ClassReference("com.adobe.customizations.ExtendedLetterEditorSkin"); 
}

Update index.mxml file to include this custom CSS file (include after including all other CSS files).

<fx:Style source="/css/custom_css.css"/>

Rebuild and redeploy the Solution template to view the changes. For information on rebuilding and redeploying, see Building and deploying the Solution Template