CSS Triangle li a

_main.css

.nav-pills > li.active > a:after{
    content:"";
    height:0;
    width:0;
    border-left: 15px solid transparent;
    border-right: 15px solid transparent;
    border-bottom: 15px solid #344364;
    position:absolute;
    bottom:0;
    left:43%;
    margin:0 0 0 -3px;
    z-index:100;
    background-color: transparent;  
    transition: all 250ms ease 0s;
    -webkit-transform: scale(0);
            transform: scale(0);
}