<!DOCTYPE html>
<head>
<style>
html {
	height: 100%;
}

body {
	display: flex;
	flex-direction: column;
	width: 600px;
    height: 500px;
    padding: 10px;
    border: 1px solid black;
}

.container {
    width: 400px;
    height: 340px;
    margin: 20px;
	flex: 1 1 0;
	overflow: scroll;
    border: 1px solid black;
}

.content {
	height: 2500px;
    background-image: repeating-linear-gradient(white, silver 300px);
}
</style>
<script>
    if (window.testRunner)
        testRunner.setRenderTreeDumpOptions(testRunner.RENDER_TREE_SHOW_OVERFLOW);
</script>
</head>
<body>
<div class="container">
	<div class="content"></div>
</div>
</body>
</html>