Example Concept: Pseudo-classes are used to define a special state of an element, such as ":hover" for when a user hovers over an element. Pseudo-elements, like "::before" and "::after", allow you to style specific parts of an element, such as adding content before or after the element's content. Pseudo-classes are written with a single colon (e.g., ":hover"), while pseudo-elements use a double colon (e.g., "::before").