.list-group .list-group-item + .sub-menu{
    display: none;
}

.list-group .list-group-item.has-submenu{
    border-bottom: 0;
}

.list-group .list-group-item + .sub-menu a:first-child{
    border-top: 0;
}

.list-group .list-group-item + .sub-menu a:last-child{
    border-bottom: 0;
}

.list-group .list-group-item.active + .sub-menu{
    display: block;
}