Selector by id and CSS classes

One element can be assigned both id and classes. In this case, part of the element's styles can be set via id, and part of the styles via the class:

<div id="block" class="large">
	<p>text</p>
	<p>text</p>
</div>

#block {
	color: red;
	font-family: Arial;
}
.large {
	font-size: 30px;
}

Style the blocks by id and by class:

<div id="block" class="text">
	<p>text</p>
	<p>text</p>
	<p>text</p>
</div>
<div class="text">
	<p>text</p>
	<p>text</p>
	<p>text</p>
</div>