.arrow_box:after {
border-color: rgba(136, 183, 213, 0);
border-bottom-color: #ffffff;
border-width: 30px;
margin-left: -30px;
}
.arrow_box:before {
border-color: rgba(194, 225, 245, 0);
border-bottom-color: #E96A4A;
border-width: 32px;
margin-left: -32px;
}
原文：http://www.cnblogs.com/dingyuanxin/p/4112527.html