What is an ID selector in CSS?

An ID selector in CSS is utilized to apply styles specifically to elements that have a unique identifier, denoted by the "#" symbol followed by the ID name. This means that when you define a style using an ID selector, it targets only one element on the page that has the specific ID assigned to it. For instance, if you have an HTML element like <div id="header">, you can apply styles using #header { color: blue; }, which will only change the text color of that particular div element.

This selectivity is essential in web development because it allows for precise control over styles without affecting other similar elements on the page. In contrast, other types of selectors, such as class selectors or universal selectors, either apply styles more broadly or to groups of elements, which can lead to conflicts or unintended styling outcomes. The distinctive nature of ID selectors underscores their importance in achieving a clean and maintainable CSS structure.