What Is a CSS Selector?

CSS relies on pattern matching rules to determine which style applies to which element in the document. These patterns are called selectors and they range from tag names (for example,

p

to match paragraph tags) to very complicated patterns that match very specific parts of a document. For example,

p#myid > b.highlight

would match any

b

tag with a class of

highlight

that is a child of the paragraph with the id

myi

A CSS selector is the part of a CSS style call that identifies what part of the web page should be styled. The selector contains one or more properties that define how the selected HTML will be styled.

There are several different types of selectors:

• type selectors – matching a specific element
• class selectors – matching elements with a specific class
• ID selectors – matching the element with a specific ID
• descendant selectors – matching elements that are descendants of a specific element
• child selectors – matching elements that are a child of the specific element
• universal selectors – matching any element
• adjacent sibling selectors – matching elements immediately preceded by a specific element
• attribute selectors – matching elements with a specific attribute or attribute value
• pseudo-class selectors – matching elements with a specific pseudo-class
• pseudo-element selectors – matching elements with specific pseudo-element properties

The format of a CSS style looks like this:

selector { style property : style ; } 

Separate multiple selectors that have the same style with commas. This is called selector grouping. For example:

selector1, selector2 { style property : style ; } 

Grouping selectors is a shorthand mechanism to keep your CSS styles compact. The above grouping would have the same effect as:

selector1 { style property : style ; }
selector2 { style property : style ; } 

Not all older browsers support all the CSS selectors. If you are setting up CSS for use with browsers as old as IE8 or older, be sure to test your selectors in as many browsers on as many operating systems as you think might be used to access your code. If you are using CSS1, CSS2, or CSS3 selectors for use with current browsers, you should be fine.