div{ border:1px solid red; margin:20px; text-align:center; } 这样写好吗？
<!DOCTYPE HTML>
<html>
<head>
<meta charset="utf-8">
<title>定宽块状元素水平居中</title>
<style>
div{
border:1px solid red;
margin:20px;
text-align:center;
}
</style>
</head>
<body>
<div>我想要在父容器中水平居中显示。</div>
<!--下面是任务部分-->
<div><img src="http://img1.sycdn.imooc.com//52da54ed0001ecfa04120172.jpg" /></div>
</body>
</html>
