index.html
style.css
<!DOCTYPE html>
<html>
<head>
<title>ID</title>
<link href="style.css" rel="stylesheet">
</head>
<body>
<h1 id="title">This heading will be red</h1>
<p>This paragraph will be black, with no ID.</p>
<p id="introduction">This paragraph will be blue.</p>
</body>
</html>#title {
color: red;
}
#introduction {
color: blue;
}