An ADF Faces application is a modern web application, so the technology used for controlling the look of the application is Cascading Style Sheets (CSS).
The idea behind CSS is that the web page (in HTML) should contain only the structure and not information about appearance. All of the visual definitions must be kept in the style sheet, and the HTML file must refer to the style sheet. This means that the same web page can be made to look completely different by applying a different style sheet to it.
In order to change the appearance of your application, you need to understand some CSS basics. If you have never worked with CSS before, you should start by reading one of the many CSS tutorials available on the Internet.
To start with, let's repeat some of the basics of CSS.
The CSS layout instructions are written in the form of rules. Each rule is in the following form:
selector { property: value; }