Joomla! Offers a possibility to overwrite not only module or component templates, but also standard CMS prompts. The prompts mentioned above are not so glamorous, so we have overwrote standard error pages, such as "404 Page not found" or "500 Internal Server Error", so as to make a template be coherent in any situation.
Additionally, we have also overwrote the prompt relevant to web's maintenance works. As a result, when browsing this mode, a user is going to see an aesthetic login script with their website's logo on it.
If you need to modify these templates, their XHTML code can be found in files as error.php (information about errors) and offline.php (web's maintenance works info) in the main template's folder. Files responsible for modeling these webs are CSS files that can be found in css/system/ folder.
Both webs above mentioned are independent websites which cannot be embedded with any modules or components.