为什么没有设置定宽和auto照样能水平居中？
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>定宽块状元素水平居中</title>
<style>
div{
border:1px solid red;
}
.center{
text-align:center;
}
</style>
</head>
<body>
<div class="center">我是定宽块状元素，我要水平居中显示。</div>
</body>
</html>
