引用元: Tryit Editor v1.8.
<!doctype html>
<html>
<head>
<style>
p:hover {
border:1px solid red;
outline-style:solid;
outline-color:#00ff00;
outline-width: 15px;
}
</style>
</head>
<body>
<p>
<b>Note:</b>
IE8 supports the outline properties only if a !DOCTYPE is specified.
</p>
</body>
</html>