Additional themes may be defined by creating a new theme directory
  containing the necessary files, as well as the corresponding XML file, whose
  name must match that of the theme's directory.
    - 
        Make a new directory within the /themes
        directory.
        Note: Do not include spaces in the directory name.
 - 
        Copy the contents of an existing theme directory to the new theme
        directory.
        
For example, copy the greenTheme directory.
 - 
        Open the following files:
        
- base.css
 - ie6.css
 - ie7.css
 - presentation.css
 - yui/assets/skin.css
 
 - Specify the new theme by searching for .yui-skin-greenTheme and replacing with .yui-skin-XXX where XXX is the name of the new theme directory.
 - Save the files.
 
The new theme is then available in the list of themes on the
        Application tool.