<html>
    <head>
        <style>
            div {
                opacity: 0.5;
                height: 50%;
                width: 50%;
            }

            body > div > div {
                background-color: green;
            }

            .composited {
                width: 100%;
                height: 50%;
            }
        </style>
    </head>
    <body>
        <div><span></span>
            <div><span></span>
                <div class="composited"><span></span></div>
            </div>
        </div>
    </body>
</html>