class: HTML elements can have one or more classes,
separated by spaces. You can style elements using CSS by selecting
them with their classes.
<div class="big-box yellow-box">This is a big yellow box.</div>
id: An HTML element can have an id attribute to
identify it. id elements should always be unique to that single
element, and each element should never have more than one id.
<div id="my-box">This is my box! Put your text in some other box.</div>