Although it isn’t required, you can give your HTML elements a unique identifier, assign them a particular class (or classes), or both. After doing so, you can apply styles to all elements with a given id or class name. That’s certainly their most popular use, but not their only one (see the tips in this section).
Within the start tag of the element, type id="name", where name uniquely identifies the element . name can be almost anything, as long as it doesn’t start with a number or contain any spaces.