This is a forum for the editor Notepad++, not whatever you happen to be using the editor for.
However, that’s an easy one: stop using smart quotes. Changing your code to the following worked for me.
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8"/>
<title>Introduction to CSS</title>
<style type="text/css">
p {
color: red;
}
</style>
</head>
<body>
<p> Style Me!</p>
<p> Style Me!</p>
</body>
</html>
