现场演示：我的 HTML 文档

<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Example of CSS outline Property Animation</title>
<style>
.animated {
	width: 200px;
	padding: 60px 0;
	margin: 100px;
	font: bold 46px sans-serif;
	background: #e6e6fa;
	outline: 5px solid #7d7de6;
	text-align: center;	
    -webkit-animation: test 4s infinite; /* Chrome, Safari, Opera */
    animation: test 4s infinite;
}
/* Chrome, Safari, Opera */
@-webkit-keyframes test {
    50% {outline: 50px solid #4b0082;}
}
/* Standard syntax */
@keyframes test {
    50% {outline: 50px solid #4b0082;}
}
</style>
</head>
<body>
	<p><strong>Warning:</strong> CSS Animations do not work in Internet Explorer 9 and earlier versions.</p>
	<p><strong>Note:</strong> Among all the individual outline properties only the outline-width, and outline-color properties are animatable in CSS. See the CSS <a href="https://www.appwang.com/css-reference/css-outline-property.php" target="_top">outline</a> shorthand property for details.<p>
	<div class="animated">Box</div>
</body>
</html>