<!DOCTYPE html>
<html>
<head>
<title>Title of the document</title>
<style>
body {
/* Set "section" to 0 */
counter-reset: section;
}
h2 {
/* Set "subsection" to 0 */
counter-reset: subsection;
}
h2::before {
counter-increment: section;
content: "Book " counter(section) ": ";
}
h3::before {
counter-increment: subsection;
content: counter(section) "." counter(subsection) " ";
}
</style>
</head>
<body>
<h2>HTML</h2>
<h3>HTML Basics</h3>
<h3>HTML Templates</h3>
<h3>HTML References</h3>
<h3>HTML Tags</h3>
<h2>CSS</h2>
<h3>CSS Basics</h3>
<h3>CSS References</h3>
<h3>CSS Advanced</h3>
<h3>CSS Guides</h3>
<h3>CSS Selectors</h3>
<h3>CSS Properties</h3>