If you know some basic CSS but wonder how the “cascade” part of Cascading Style Sheets works, here is a useful guide.
Actually, this is a 73-page, two-chapter excerpt from the upcoming fourth edition of Eric A. Meyer’s CSS: The Definitive Guide. If you are learning CSS, dealing with CSS issues, or moving to CSS3, this small book can provide you with numerous how-to examples to apply to right now.
The first chapter focuses on “Selectors.” Selectors are not clearly defined at the beginning. But they generally are described elsewhere as “patterns” that can be used to select the element or elements you want to style in a document, such as headings of a certain font sizes or paragraphs with text in specific colors.
Fortunately, the first chapter’s code examples, descriptive paragraphs, and illustrations quickly clarify how to put selectors to work in a document. “[D]ocument structure and CSS selectors allow you to apply a wide variety of style to elements,” the author notes.
The second chapter’s topics are “Specificity and the Cascade.” And the initial technical definitions get a bit dense. For example: “When determining which values should apply to an element, a user agent must consider not only inheritance but also the specificity of the declaration, as well as the origin of the declarations themselves. The process of consideration is what’s known as the cascade.”
Once again, fortunately, the second chapter’s code samples, illustrations, and follow-up paragraphs quickly clarify what is going on. And they enable you to learn by doing, seeing the outcome, and applying what you’ve learned to documents of your own.
— Si Dunn