Exploring Styles in FileMaker 13
A PEEK UNDER THE THEMES HOOD:
It is true that FileMaker handles some themes and styles in CSS. So yes, there is really CSS that is used. You don’t have to worry about learning CSS, because the interface for managing everything is part of the updated inspector (Appearance pane) that gives unprecedented access to all the formatting elements associated with parts and objects on a layout, including fields and text.
There’s a lot to learn about Themes and Styles, and hopefully more to come in future FM versions.