What do the :first-child and :last-child selectors do in CSS?

The :first-child and :last-child selectors are designed to specifically target and style the first and last child elements within a parent element, respectively. This means that if a parent element contains several child elements, the :first-child selector will apply styles only to the very first child, while the :last-child selector will apply styles only to the very last child. This selective targeting is useful when you want to customize the appearance of specific elements in a list or group without needing to add classes or IDs.

The other options do not accurately describe the functionality of these selectors. For example, styling only the first and last parent elements is not within their scope, as these selectors work on child elements. Similarly, applying styles to all child elements of a parent is not the purpose of these pseudo-classes, and they certainly do not remove elements from the document entirely, which is outside the capabilities of CSS. The correct option effectively captures the specific and targeted functionality of these selectors in CSS.