ID Implementation Example CSS | Attribute Class Vs. Id pada HTML

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>ID</title>
    <style>
        #black-box {
            background: black;
            color: white;
            height: 50px;
        }
    </style>
</head>
<body>
    <div id="black-box">Element with ID.</div>
    <div >Element lain!</div>
</body>
</html>