This chapter is from the book
Naming Elements
You can give your HTML elements either a unique name or one that identifies them as belonging to a particular class. You can then apply styles to all elements with a given name.
To name unique elements
Within the opening tag of the element, type id="name", where name uniquely identifies the element.
To name groups of elements
Within the opening tag of the element, type class="name", where name is the identifying name of the class.