Part III: The Presentation Layer: Cascading Style Sheets

Chapter 16. Cascading Style Sheets Fundamentals

Cascading Style Sheets (CSS) is a W3C standard for defining the presentation of web documents. Presentation refers to the way a document is displayed or delivered to the user , whether it's on a computer monitor, a cell phone display, or read aloud by a screen reader. This book focuses primarily on the visual aspects of presentation, such as typography, colors, alignment, layout, and so on. CSS is the mechanism for providing these types of style instructions to elements in a document that has been marked up with XHTML, HTML, or any XML language. Most important, CSS keeps these presentation instructions separate from the content and its structural and semantic markup.

Before CSS, web designers were at the mercy of the browser's rendering engine and internal style sheets for the way HTML elements looked in the browser window. Presentational elements and attributes added to HTML, such as the font tag and the bgcolor attribute, granted some additional control over visual display, but the integrity of markup suffered. Cascading Style Sheets (or just "style sheets" in these chapters) hand visual display decisions back to designers and authors. This comes as good news both for designers who want more control over presentation and for those who are eager to see HTML get back to the exclusive business of defining document structure and meaning. Style sheets make both of these goals possible.

16.1. CSS in a Nutshell

The chapters in this section provide a solid overview and reference of CSS and its properties. This book focuses on CSS used with documents written in (X)HTML, although CSS can also be used with any XML language.

This chapter lays an important foundation for understanding how CSS works, including rule syntax and how style sheets are applied to documents. It also covers some critical key concepts at the core of CSS, such as inheritance, handling conflicting styles (the cascade), how elements display, and the box model. Browser issues are briefly addressed as well. The chapter finishes with a section on specifying values in CSS.

Chapter 17 explains all the various ways elements can be targeted for style application, and Chapters 18 through 23 cover the CSS visual display properties as they are specified in the CSS 2.1 Recommendation. These chapters document how CSS is designed to work. Browser support varies, of course, so this book provides notes if a property or its values are particularly problematic in a browser.

Finally, Chapters 24 and 25 put everything together in real-world applications. Chapter 24 is a cookbook of some of the most popular CSS techniques, such as CSS rollovers and multicolumn layouts. All of the browser- related problems and solutions are aggregated in Chapter 25, making it a handy reference if you encounter problems down the road.

In the interest of keeping everything "in a nutshell," the chapters in this section stick to visual media properties. The CSS properties related to interface, paged media, and aural (speech) media are included in Appendix B.