9.26百度一面凉经

请用flex实现九宫格布局
1，九宫格依次用数字1-9居中填充
2，内部井字分割线
html
<div class = 'gridBox'>
  <div class='cellLi'>1</div>
    <div class='cellLi'>2</div>
    <div class='cellLi'>3</div>
    <div class='cellLi'>4</div>
    <div class='cellLi'>5</div>
    <div class='cellLi'>6</div>
    <div class='cellLi'>7</div>
    <div class='cellLi'>8</div>
    <div class='cellLi'>9</div>
</div>
css
.gridBox{
    background-color: red;
    overflow:hidden;
    margin:20px 0;
    display:flex;
    flex-wrap:wrap;
}
.cellLi{
    width:calc(100%/3);
    padding:60px 0;
   text-align:center;
    border:1px solid #f5f5f5;
    box-sizing:border-box;
    background-color: #fff;
}