用css3 after伪类写三角形

.ys_c_sub{
                  position:absolute;
                    top:-50%;
                    right:100%;
                    width:200px;
                    background:#fff;
                    padding:10px;
                    box-shadow:0px 0px 8px #999;
                }
                .ys_c_sub:after{
                    content: '';
                      position: absolute;
                      top: 40%;
                      right:-20px;
                      border: 10px solid transparent;
                      border-left-color: #fff;
                }