<!DOCTYPE html>

<html>
<head>
    <style>
        #indicator {
            position: absolute;
            top: 20px;
            left: 20px;
            width: 200px;
            height: 200px;
            background-color: red;
        }
        
        .container {
            position: absolute;
            top: 20px;
            left: 20px;
        }

        .solid-background {
            position: relative;
            float: left;
            width: 200px;
            height: 200px;
            background-color: green;
            z-index: 0;
        }
        
        #scrollable {
            width: 100%;
            height: 100%;
            overflow: hidden;
        }
        
        .opaque {
            background-color: gray;
            width: 100%;
            height: 100%;
        }
        
        .non-opaque {
            background-color: transparent;
            width: 100%;
            height: 100%;
        }
    </style>
    <script>
        window.addEventListener('load', function() {
            document.getElementById('scrollable').scrollTop = 200;
        }, false);
    </script>
</head>
<body>

<div id="indicator"></div>

<div class="container">
    <div class="solid-background">
        <div id="scrollable">
            <div class="opaque">
            </div>
            <div class="non-opaque">
            </div>
        </div>
    </div>
</div>

</body>
</html>