<!DOCTYPE html>
<html>
<head>
    <style>
        .container {
            position: absolute;
            margin: 40px;
            padding: 50px;
            width: 400px;
            height: 300px;
            border: 1px solid black;
        }
        
        .caption-container {
            position: absolute;
            top: 0;
            left: 0;
            width: 100%;
            height: 100%;
            box-shadow: 0 0 10px black;
        }
        
        .caption {
            position: absolute;
            width: 300px;
            bottom: 20px;            
            text-align: center;
            height: 100px;
            background-color: blue;
        }
        
        .child {
            position: absolute;
            top: 10px;
            left: 320px;
            width: 100px;
            height: 100px;
            background-color: blue;
        }
        .composited {
            transform: translateZ(0);
            background-color: silver;
        }
    </style>
</head>
<body>
    <div class="container">
        <div class="composited">composited</div>

        <div class="caption-container">
            <div class="caption">
                This should move, not duplicate
                <div class="child">
                    child
                </div>
            </div>
        </div>
    </div>
</body>
</html>