試一試 - CSS Reference animation-duration

<!DOCTYPE html>
<html>
<head>
<style>
div {
   width: 100px;
   height: 100px;
   background: red;
   position: relative;
   -webkit-animation: mymove infinite; /* Chrome, Safari, Opera */
   -webkit-animation-duration: 2s; /* Chrome, Safari, Opera */
   animation: mymove infinite;
   animation-duration: 2s;
}

/* Chrome, Safari, Opera */
@-webkit-keyframes mymove {
   from {top: 0px;}
   to {top: 200px;}
}

@keyframes mymove {
   from {top: 0px;}
   to {top: 200px;}
}
</style>
</head>
<body>

<p><strong>Note:</strong> The animation-duration property is not supported in Internet Explorer 9 and earlier versions.</p>
<div></div>
<p><b>Note:</b> Always specify the animation-duration property. Otherwise the duration is 0, and the animation will not be played.</p>

</body>
</html>