<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<style>
.arrow {
width:0;
height:0;
position: absolute;
top:0;
left:0;
display: inline-block;
}
.arrow-down {
border-left:5px solid transparent;
border-right:5px solid transparent;
border-top:5px solid #f63;
}
.arrow-up {
border-bottom:5px solid #f63;
border-left:5px solid transparent;
border-right:5px solid transparent;
top:50px;
}
.arrow-left {
border-top:5px solid transparent;
border-bottom:5px solid transparent;
border-right:5px solid #f63;
top:100px;
}
.arrow-right {
border-top:5px solid transparent;
border-bottom:5px solid transparent;
border-left:5px solid #288;
top:150px;
}
</style>
</head>
<body>
<div style="position: relative">
<span class="arrow arrow-down"></span>
<span class="arrow arrow-up"></span>
<span class="arrow arrow-left"></span>
<span class="arrow arrow-right"></span>
</div>
</body>
</html>
补充：css生成三角形：http://www.sucaihuo.com/tools/triangle