An Internal CSS style sheet is used to format the single HTML Page with the unique style.
The internal style is defined inside the <style> element and this tag inside the head section.
Example :
<!DOCTYPE html>
<html>
<head>
<style>
body {
background-color: aliceblue;
}
h1 {
color: tomato;
margin-left: 20px;
}
</style>
</head>
<body>
<h1>This is a heading</h1>
<p>This is a paragraph.</p>
</body>
</html>