less - 循环 loop

.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);