<!DOCTYPE html>
<html>
<head>
    <style>
        .stage {
            margin: 20px;
            width: 300px; height: 250px;
            border: 2px solid black;
            transform-style: preserve-3d;
        }
        
        .slide {
            width: 100%;
            height: 100%;
            animation-duration: 20ms;
            animation-fill-mode: forwards;
            -webkit-backface-visibility: hidden;
            background-color: blue;
        }
        
        .animating {
            animation-name: slide;
        }
        
        @keyframes slide {
            0% {   transform-origin: 50% 50%; transform: translateX(400px); } 
            50% {  transform-origin: 50% 50%; transform: translateX(0px); } 
            100% { transform-origin: 50% 50%; transform: translateX(0px); }             
        }
    </style>
    <script>
        if (window.testRunner)
            testRunner.waitUntilDone();

        function animationEnded()
        {
            if (window.testRunner)
                testRunner.notifyDone();
        }

        window.addEventListener('load', () => {
            document.getElementById('target').classList.add('animating');
        }, false);
    </script>
</head>
<body>
    <div class="stage">
        <div id="target" class="slide" onanimationend="animationEnded()"></div>
    </div>
</body>
</html>