While you should only depend on features that are documented explicitly, you can gain valuable insight into the structure of a BUI web page using the web inspector built into your browser. For example, refer to the BUI ShowcaseEdit Controls sample. In Google Chrome, right-click on any element and select "Inspect Element":
The inspector provides a wealth of information about how the browser has rendered the element on the page, and how it has interpreted the associated CSS rules, including any custom CSS defined by the developer. This can be particularly valuable when you are defining new CSS rules and they aren't working as expected.