What is a CSS selector?

A CSS selector is a pattern used to select HTML elements that you want to style with CSS. When writing CSS, the selector specifies which elements on the webpage will have the associated styles applied to them. This allows developers to target specific elements based on their types, classes, IDs, attributes, or relationships to other elements.

For example, if you want to change the color of all paragraphs in a document, you would use the p selector to apply styles directly to all <p> tags. This fundamental concept in CSS enables precise control over presentation and layout in web development.

The other options do not accurately define a CSS selector. While media queries are related to responsive design by allowing different styles for different screen sizes, they do not define elements. Similarly, declaring HTML elements or creating responsive designs involves more than just selecting them; it involves using various techniques and structures in HTML and CSS together.