Understanding pseudo-elements and pseudo-classes is a must for any CSS practitioner. Pseudo-elements are keywords added to selectors that let you style a specific part of the selected element(s).  They include: ::before - inserts content before the content of the selected element ::after - inserts content after the content of the selected element ::first-letter - selects the first letter of each element ::first-line - selects the first line of each element ::selection - applies styles to the part of a document that the user has highlighted Pseudo-classes, on the other hand, are used to define a special state of an element. Here are some commonly used pseudo-classes: :visited - selects all visited links :hover - selects elements when you mouse over them :active - selects the active link :focus - selects the input field currently in focus These powerful tools in your CSS toolbox can make your designs much more dynamic and interactive.