flex九宫格

重要的是justify-content: center;和align-items: center;
父元素设置flex-wrap: wrap;换行，设置宽高。


<!DOCTYPE html>
<html>
<style>
    .box{
        display:flex;
        width: 300px;
        height: 300px;
        border: 1px solid #f00;
        flex-wrap: wrap;
        justify-content: center;
        align-items: center;
        margin-top: 100px;
        margin-left: 100px;
    }
    .item{
        display: flex;
        /*flex-direction: column;*/
        width: 80px;
        height: 80px;
        background-color: #890;
        border: 1px solid #000000;
        justify-content: center;
        align-items: center;
    }
</style>
<body>
<div class="box">
    <div class="item">1</div>
    <div class="item">2</div>
    <div class="item">3</div>
    <div class="item">4</div>
    <div class="item">5</div>
    <div class="item">6</div>
    <div class="item">7</div>
    <div class="item">8</div>
    <div class="item">9</div>
</div>
</body>
</html>