This video looks at how Joomla 3 enables users to edit template files directly (including css and php files), it also looks at how to create overrides for components and modules to display in your own custom style (advanced users only).
source
Joomla 3 How to edit template css/php files, create overrides of component layouts
Joomla 3 How to edit template css/php files, create overrides of component layouts
