The Simple theme is used within the tutorials on docs.silverstripe.org. Providing developers with real examples of how themes can be customised and altered to each specific need.
You are welcome to customise and re-use this theme for your own personal or business use. Changing the theme requires uploading a new theme into the file structure of the site, which usually requires some technical knowledge. Once a new theme has been added, website administrators can switch themes within the setting area of the CMS.