CSS or Cascading Style Sheet is another markup language that allows you to fine-tune the aesthetics of the HTML files.
<!-- Demonstrates inline CSS -->
<!DOCTYPE html>
<html lang="en">
<head>
<title>Webpage - Title</title>
</head>
<body style="text-align: center">
<header style="font-size: large">
Hello World!
</header>
<main style="font-size: medium">
Homepage
</main>
<footer style="font-size: small">
Copyright © all rights reserved.
</footer>
</body>
<!DOCTYPE html>
<!-- Demonstrates external CSS -->
<html lang="en">
<head>
<link href="style.css" rel="stylesheet">
<title>css</title>
</head>
<body class="centered">
<header class="large">
Hello World!
</header>
<main class="medium">
Homepage
</main>
<footer class="small">
Copyright © all rights reserved.
</footer>
</body>
</html>