.triangle_index_volume {
    position: relative;
}
.triangle_index_volume:after {
    position: absolute;
    right: 6px;
    top: 23px;
    width: 0;
    height: 0;
    content: "";
    border-width: 5px 5px 0 5px;
    border-style: solid;
    border-color: #000 transparent;
    -webkit-transition: all .25s;
       -moz-transition: all .25s;
        -ms-transition: all .25s;
         -o-transition: all .25s;
            transition: all .25s;
}

.triangle_index_volume.active:after{       
    top: 12px;
    -webkit-transform: rotate(180deg);
       -moz-transform: rotate(180deg);
        -ms-transform: rotate(180deg);
         -o-transform: rotate(180deg);
            transform: rotate(180deg); 
}