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>