<!DOCTYPE html>

<html>
<head>
    <style>
        body {
            height: 10000px;
            width: 10000px;
            margin: 0;
        }
        .box {
            position: absolute;
            background-color: rgba(0, 0, 0, 0.5);
            border: 5px solid black;
            box-sizing: border-box;
        }
        
        .width {
            width: 100px;
            height: 100px;
            padding-left: 100px;
        }

        .height {
            height: 100px;
            width: 100px;
            padding-top: 100px;
        }
        
        body.changed .height {
            height: 100vh;
        }

        body.changed .width {
            width: 100vw;
        }
    </style>
    <script>
        if (window.testRunner)
            testRunner.waitUntilDone();

        function doTest()
        {
            window.setTimeout(function() {
                document.body.classList.add('changed');
                if (window.testRunner)
                    testRunner.notifyDone();
            }, 0);
        }
        window.addEventListener('load', doTest, false);
    </script>
</head>
<body>
<div class="box width">
    This should be as wide as the CSS viewport.
</div>

<div id="vertical" class="box height">
    This should be as tall as the CSS viewport.
</div>
</body>
</html>