html5css3:盒子内减属性

<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title>盒子内减属性</title>
		<style type="text/css">
			div{width:300px;height:300px;background:pink;margin:30px auto;
			border-radius:15px; box-shadow: 2px 2px 2px 2px #CCCCCC;}
			div:first-child{padding:30px;}
			div:last-child{
				padding:30px;
				box-sizing:border-box;
			}
		</style>
	</head>
	<body>
		<div></div>
		<div></div>
	</body>
</html>

实战小案例：

<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title>利用伪类去做鼠标放上去出现边框</title>
		<style type="text/css">
			div{width:220px;height:250px;margin:20px auto;border-radius:15px;position:relative;overflow: hidden;}
			div:hover:after{
				content:"";
				position:absolute;
				top:0;
				left:0;
				width:100%;
				height:100%;
				border:10px solid rgba(111,111,111,0.5);
				border-radius:15px;
				box-sizing: border-box; /* 盒子内减属性 */
			}
		</style>
	</head>
	<body>
		<div><img src="img/ldh.jpg"/></div>
		<div><img src="img/ldh.jpg"/></div>
		<div><img src="img/ldh.jpg"/></div>
		<div><img src="img/ldh.jpg"/></div>
		<div><img src="img/ldh.jpg"/></div>
	</body>
</html>