 <p><strong>id:</strong> </p> <p>It will identify the unique element of your entire page. No other element should be declared with the same id. The id selector is used to specify a style for a single, unique element. The id selector uses the id attribute of the HTML element, and is defined with a "#".</p> <p><strong>class:</strong></p> <p>The class selector is used to specify a style for a group of elements. Unlike the id selector, the class selector is most often used on several elements. </p> <p>This allows you to set a particular style for many HTML elements with the same class. </p> <p>The class selector uses the HTML class attribute, and is defined with a "."</p>