affter before 的使用列子
<style>
body{padding:100px;}
.box{width:200px; height:100px; background:#777; line-height:100px; text-align:center;}
a{position:relative;text-decoration:none; display:inline-block; width:100px; height:30px; background:greenyellow;
line-height:30px; text-align:center; color:#fff;}
a:hover:before,a:hover:after{
position:absolute;color:red; font-size:20px;
}
a:hover:before{content:'['; left:-10px; }
a:hover:after{content:']'; right:-10px;}
</style>
<div class="box">
<a href="#">lalallala</a>
</div>
<!DOCTYPE html>
<html lang="en">
<head>
<title>Demo</title>
<style>
.boimg{
border: 6px solid #fff;
width: 400px;
height:225px;
margin: 50px;
position: relative;
box-shadow: 2px 2px 5px rgba(0,0,0,0.3);
}
.boimg img{width:100%;heigth:100%;}
.boimg:before,.boimg:after {
content: "";
width: 400px;
height:225px;
background: #aaa;
border: 6px solid #fff;
position:absolute;
z-index:-1;
top:0;
left:-10px;
box-shadow: 2px 2px 5px rgba(0,0,0,0.3);
transform: rotate(-5deg);
}
.boimg:after {
top:5px;
left:0;
transform: rotate(3deg);
}
</style>
</head>
<body>
<div class="shbox" style="background:none;">
<div class="boimg">
<img src="https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1522834445084&di=376ed78bccfc705f2601b73956199600&imgtype=0&src=http%3A%2F%2Fimg2015.zdface.com%2F20170623%2F25985f40a751689774e53c2e16f266ee.jpg" />
<div>
</div>
</div>
</div>
</body>
</html>
<!DOCTYPE html>
<html lang="en">
<head>
<title>Demo</title>
<style>
.boimg{
border: 6px solid #fff;
width: 400px;
height:225px;
margin: 50px;
position: relative;
box-shadow: 2px 2px 5px rgba(0,0,0,0.3);
}
.boimg img{width:100%;heigth:100%;}
.boimg:before,.boimg:after {
content: "";
width: 400px;
height:225px;
background: #aaa;
border: 6px solid #fff;
position:absolute;
z-index:-1;
top:0;
left:-10px;
box-shadow: 2px 2px 5px rgba(0,0,0,0.3);
transform: rotate(-5deg);
}
.boimg:after {
top:5px;
left:0;
transform: rotate(3deg);
}
</style>
</head>
<body>
<div class="shbox" style="background:none;">
<div class="boimg">
<img src="https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1522834445084&di=376ed78bccfc705f2601b73956199600&imgtype=0&src=http%3A%2F%2Fimg2015.zdface.com%2F20170623%2F25985f40a751689774e53c2e16f266ee.jpg" />
<div>
</div>
</div>
</div>
</body>
</html>