关于css3:CSS3-nthchild-选择器-卡片布局的应用

某些卡片布局时有时为了让元素不超出外框，管制最初一列，最初一行
如图：

.operate-wrap {
  font-size: 0;
  width: 140px;
  border: 2px #444 solid;
  .item {
    font-size: 12px;
    width: 30px;
    display: inline-block;
    padding: 0;
    margin: 0 10px 5px 0;
    border: 5px #97ae6a solid;
    &:nth-child(3n) {
      border: 5px blue solid;
      margin-right: 0;
      background-color: #ff0000;
    }
    &:nth-last-child(-n+3) {
      margin-bottom: 0;
      background-color: #fff000;
    }

    <div class="operate-wrap">
      <div class="item">1</div>
      <div class="item">1</div>
      <div class="item">1</div>
      <div class="item">1</div>
      <div class="item">1</div>
      <div class="item">1</div>
      <div class="item">1</div>
      <div class="item">1</div>
      <div class="item">1</div>
      <div class="item">1</div>
      <div class="item">1</div>
      <div class="item">1</div>
    </div>