demo
<!DOCTYPE html>
<html lang="zh">
<head>
<meta charset=utf-8>
<title>demo</title>
</head> <style>
#demo{
width:100px;
height:100px;
border:2px solid #000;
}
#demo:before{
content:'';
display:block;
width:0;
height:0;
position:relative;
top:10px;
left:100px;
border-left:9px solid #000;
border-top:7px solid transparent;
border-bottom:7px solid transparent;
}
#demo:after{
content:'';
display:block;
width:0;
height:0;
position:relative;
top:-2px;
left:100px;
border-left:7px solid #fff;
border-top:5px solid transparent;
border-bottom:5px solid transparent;
}
#s{
width:0;
height:0;
border-left:20px solid transparent; /*→*/
border-right:20px solid transparent; /*←*/
border-top:20px solid transparent; /*↓*/
border-bottom:20px solid green; /*↑*/
}
</style>
<body>
<div id='demo'></div> <div id="s"></div>
</body>
</html>