1.body代码：

<div id="test">
  <a><div>1</div>
</a>
  <a><div>2</div>
</a>
  <a><div>3</div>
</a>
  <a><div>4</div>
</a>
  <a><div>5</div>
</a>
  <a><div>6</div>
</a>
  <a><div>7</div>
</a>
  <a><div>8</div>
</a>
  <a><div>9</div>
</a>
</div>

2.css. 

#test div{
  width: calc(100% - 13px);
  line-height: 50px;
  text-align:center;
  background: #AAA;
  margin-top: 13px;
}
#test a{
  width: calc((100% - 13px) / 3);     //如果是6宫格，就➗2 就可以了
  line-height: 55px;
  float: left;
  text-decoration: none;
  padding-left: 13px;
  padding-bottom: 13px;
  margin-right: -13px;
  margin-bottom: -13px;
}
#test a:hover{
  background: red;
}