ul>li::after,ul>li::before{ position: absolute }
ul>li::after{right:0px bottom:0px content:"" background:url() no-repeat}
ul>li::before{left:0px top:0px content:"" background:url() no-repeat} <ul>
<li>
曾经我以为我很完美，唯一的缺点是代码写太溜，直到有一天，一群女孩围着我说“你代码写得好溜啊！”，我说“写得溜有什么用，又没人采纳”，她们确骂我，说“你张这么帅，代码还写这么溜，哪个会不采纳你的！”
</li>
</ul>
<html><head>
<meta http-equiv="Content-Type" content="text/html charset=UTF-8">
<title>无标题文档</title>
<style type="text/css">
body,html{
margin:0px
height:100%
}
.autoHeight{
width:100px
height:100%
background:red
}
</style>
<style type="text/css">
div{ background: #FFF
font-family: "微软雅黑"
top: 10%
position: absolute
left: 50%
display: inline-block
padding: 10px
border-radius: 10px
box-shadow: 1px 1px 3px rgba(0,0,0,0.2)}
div:before {
left: -10px
top: 50%
margin-top: -6px
position: absolute
z-index: -1
content: ""
width: 0
height: 0
border-top: 8px solid transparent
border-bottom: 8px solid transparent
border-right: 11px solid rgba(0, 0, 0, 0.1)
border-left: 0
}
div:after {
left: -11px
top: 50%
margin-top: -8px
position: absolute
content: ""
width: 0
height: 0
border-top: 8px solid transparent
border-bottom: 8px solid transparent
border-right: 11px solid #FFF
border-left: 0
}</style></head>
<body style="
background: #369
">
<div>你好</div>
</body>
</html>
根据你的图做的，应该合适了。
