.avatar-loop(@n, @i:1, @level) when (@i <= @n) {    &:nth-child(@{level}) .item.item-@{i} {        .avatar {            background-position: (-190px * (@i - 1) - 10px * (@i - 1)) (-190px * (@level - 1) - 10px * (@level - 1));        }    }    .avatar-loop(@n, (@i + 1), @level);}.avatar-loop(4, 1, 1);.avatar-loop(4, 1, 2);.avatar-loop(4, 1, 3);.avatar-loop(4, 1, 4);