现场演示：我的 HTML 文档

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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Example of CSS min-width Property Animation</title>
<style>
.animated {
    width: 150px;
    padding: 40px 0;
    font: bold 46px sans-serif;
    text-align: center;
    background: #aaccaa;    
    border: 1px solid #63a063;
    -webkit-animation: test 4s infinite; /* Chrome, Safari, Opera */
    animation: test 4s infinite;
}
/* Chrome, Safari, Opera */
@-webkit-keyframes test {
    50% {min-width: 500px;}
}
/* Standard syntax */
@keyframes test {
    50% {min-width: 500px;}
}
</style>
</head>
<body>
    <p><strong>Warning:</strong> CSS Animations do not work in Internet Explorer 9 and earlier versions.</p>
    <p><strong>Note:</strong> The min-width property of the following DIV box is animating from its initial value "none" to "500px", and back to the initial value "none" again up to infinite times. The min-width property overrides the width property of the element.<p>
    <div class="animated">Box</div>
</body>
</html>