What is a CSS Pseudo-Element Selector?

The CSS pseudo-element selectors are selectors that are arrangements of content within the HTML document that make up a form of undefined element. The pseudo-element selectors are:

• :after matches after an element, to place generated content.
• :before matches before an element, to place generated content.
• :first-letter matches the first letter of an element.
• :hover matches the first line of text of an element.

To style the first letter of a paragraph with a larger cap:

p:first-letter {
font-size : 2.5em ;
}

Or to add a semi-colon after every list item:

li:after {
content : ";" ;
}