test/test-css-id.html

<html>

    <head>

        <style type='text/css'>
            body{
                color: gray;
            }

            .blue{
                color: blue;
            }
            #green{
                color: green;
            }
           
            div{
                margin: 2em;
            }
            div.zwei > p {
                display:inline;
            }

            #drei > p > span{
                color:red;
            }
            
        </style>

    </head>

<body>
    Standardfarbe: grau

    <div id='eins'>
        grau <p class='blue'>blau <span id='green'>gruen</span> blau</p>
    </div>

</body>
</html>