Web Design in a Nutshell, 3rd Edition

Contextual Selectors

Type selectors, such as those in the previous example, apply to all instances of that element found in a document. By contrast, contextual selectors allow you to apply style properties to select elements, based on their context or relation to another element. There are several types of contextual selectors: descendant, child, and adjacent sibling. This is where being familiar with the document tree structure of your document comes in handy.

Contextual selectors use a specific character to signify the type of relationship between the elements in the selectors. This character is known as the combinator.