css as plugin

[eluser]xwero[/eluser]
A plugin is less overkill because it doesn't changes the core of the application. Having an easy way to add the css and image path is trivial as you don't have to do it in php. You can use the base tag for relative asset paths.

If the style sheet changes use a default setting in the config and change it if needed.

Extending classes is an option you have to think about as last option.