.up_white_nabla {
    width: 0px;
    height: 0px;
    position: relative;
    top : 7px;
    border-bottom:10px solid white;
    border-left: 10px solid transparent;
    border-right: 10px solid transparent;
}
.down_white_nabla {
    width: 0px;
    height: 0px;
    position: relative;
    top : 7px;
    border-top: 10px solid white;
    border-left: 10px solid transparent;
    border-right: 10px solid transparent;
}