先来看一下效果，这在CSS3之前，完全是不可想象的，只有图片才能做的到，但在HTML5和CSS3大行其道的今天，实现这种效果，那都不是事啊。
看一下实现的代码：
<!DOCTYPE html>
<html>
<head>
<style type='text/css'>
.arrow-up {
width: 0;
height: 0;
border-left: 20px solid transparent;
border-right: 20px solid transparent;
border-bottom: 20px solid green;
}
.arrow-down {
width: 0;
height: 0;
border-left: 20px solid transparent;
border-right: 20px solid transparent;
border-top: 20px solid orange;
}
.arrow-right {
width: 0;
height: 0;
border-top: 60px solid transparent;
border-bottom: 60px solid transparent;
border-left: 60px solid blue;
}
.arrow-left {
width: 0;
height: 0;
border-top: 10px solid transparent;
border-bottom: 10px solid transparent;
border-right: 10px solid silver;
}
</style>
</head>
<body>
<div class="arrow-up"></div>
<div class="arrow-down"></div>
<div class="arrow-left"></div>
<div class="arrow-right"></div>
</body>
</html>
