revision:
The class attribute is mostly used to point to a class in a style sheet. However, it can also be used by JavaScript (via the HTML DOM) to make changes to HTML elements with a specified class.
It can be used on any HTML element.s The class name is case sensitive! Name of a class can be used with multiple elements in an HTML document.
<element class="classname">
classname specifies one or more class names for an element. To specify multiple classes, separate the class names with a space, e.g. <span class="left important">. This allows to combine several CSS classes for one HTML element.
Naming rules are as follows: must begin with a letter A-Z or a-z, and can be followed by: letters (A-Za-z), digits (0-9), hyphens ("-"), and underscores ("_")
A paragraph.
Note that this is an important paragraph. :)
<h4 class="intro" style="margin-left:3vw;">Header 4</h4>
<p class="spec">A paragraph.</p>
<p class="important spec">Note that this is an important paragraph. :)</p>
<style>
h4.intro {color: blue;}
p.important {color: green;}
</style>
<h4 style="margin-left:3vw;" class="city main">London</h4>
<h4 style="margin-left:3vw;" class="city">Paris</h4>
<h4 style="margin-left:3vw;" class="city">Tokyo</h4>
<style>
.city { background-color: tomato; color: white; padding: 10px;}
.main { text-align: center;}
</style>