Naming Elements with a Class or ID
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).
To name an element with a unique id
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.