#colorNav ul li:first-child:before {
content: ‘‘;
position: absolute;
width: 1px;
height: 1px;
border: 5px solid transparent;
border-bottom-color: #313131;
left: 83%;
top: -10px;
margin-left: -5px;
}
原文：http://www.cnblogs.com/dingyuanxin/p/4076629.html