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Lesson 26

CSS3: Part I

Just like HTML, CSS is evolving over time. The latest version of CSS is called CSS3 and adds several important modules to CSS that will be explored over the next two lessons.

Nothing fundamental has changed with CSS in version 3: The language still uses selectors to identify elements and still allows a set of stylistic properties to be defined for these elements. CSS3 is important, however, because it specifies a number of new selectors style properties. Together, these selectors and properties greatly improve the expressiveness of CSS.

Unlike with HTML, you may have noticed that it is not necessary to specify which version of CSS you are using. CSS3 is entirely backwards compatible; therefore, if you want to use CSS3 features, you simply include them in your existing style sheets, and the browser will simply ignore them if it does not support them.

The next two lessons will not provide an exhaustive introduction to CSS3, but they will introduce the most interesting features, and will further help consolidate your knowledge of CSS.

Selectors

CSS3 provides a number of new selectors for selecting elements based on a wider set of criteria.

CSS3 includes one new operator called the tilde operator. This is used to select elements that are siblings of a specified element, and are declared anywhere after that element. For instance, in contacts.css, you might want to style tfoot elements differently if they have a sibling ­element of type thead; this could ...