less类型伪类选择器这样写为什么没用

Question

用的less伪类选择器这样写为什么没效果

  <div class="operate-wrap">
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
  </div>
  .operate-wrap {
    .item {
      display: flex;
      justify-content: space-around;
      padding: 0px 0;
      border-right: 1px #97ae6a dashed;
      &:nth-child(3n) {
        border-right: 1px #000 dashed;
      }
    }
  }

Answer 1

有效果的，线太细了设粗一点就看见了
https://codesandbox.io/s/roma...