<!DOCTYPE html>
<html>
<head>
	<title>Margin</title>
	<meta charset="utf-8">
	<style>
	body {
		counter-reset: section;
	}
	h1 {
		counter-reset: subsection;
	}
	h1:before {
		counter-increment: section;
		content: "Section " counter(section) ". ";
	}
	h2:before {
		counter-increment: subsection;
		content: counter(section) "." counter(subsection) " ";
	}
</style>
</head>
<body>
	<h1>Học HTML cơ bản</h1>
	<h2>Giới thiệu về HTML</h2>
	<h2>HTML là gì?</h2>
	<h2>Cú pháp HTML</h2>

	<h1>Học CSS cơ bản</h1>
	<h2>Giới thiệu về CSS</h2>
	<h2>CSS là gì?</h2>
	<h2>Cú pháp CSS</h2>
</body>
</html>

External CSS

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External JavaScript

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