<!DOCTYPE html>
<html>
<head>
    <title>The green box should not disappear</title>
    <style>
        .box {
            width: 400px;
            background-color: green;
            height: 0px;
            opacity: 0.8;
            transition: opacity 0.1s;
        }
        
        body.changed .box {
            opacity: 1;
        }
        
        .content {
            height: 200px;
            width: 200px;
            background-color: green;
        }
    </style>
    <script>
        if (window.testRunner)
            testRunner.waitUntilDone();

        window.addEventListener('load', () => {
            
            let box = document.getElementsByClassName('box')[0];
            box.addEventListener('transitionend', () => {
                if (window.testRunner)
                    testRunner.notifyDone();
            }, false);
            setTimeout(() => {
                document.body.classList.add('changed');
            }, 0);
        }, false);
    </script>
</head>
<body>
    <div class="box">
        <div class="content"></div>
    </div>
</body>
</html>