They are used to select parts of a web page that don’t have tags but are easy to identify, like the first line of a paragraph or a link as mouse is moved over it.
They represent change in styling based on dynamic events like a mouse click or mouse roll over in the web page which is not easily done by other means. It styles a specific state of the target element like a visited hyperlink. They have a single colon before the pseudo-class property. The order in which dynamic pseudo-classes appear in the style sheet is important due to the cascade in CSS.
