关于css垂直水平居中的几种方法

<div class="box box1">
    <span class="test">垂直居中</span>
</div>
<style>
    .box{
        width: 200px;
        height: 200px;
        border:1px solid red;
    }
    .box1{
        display: table-cell;
        vertical-align: middle;
        text-align: center;
    }
    .test{
        width: 30px;
        height: 30px;
        border:1px solid black;
    }
</style>

<div class="box box1">
    <div class="test"></div>
</div>
<style>
    .box{
        display: flex;
        justify-content: center;
        align-items: center;
        width: 200px;
        height: 200px;
        border:1px solid red;
    }
    .test{
        width: 30px;
        height: 30px;
        border:1px solid black;
    }
</style>

<div class="box box1">
    <div class="test"></div>
</div>
<style>
    .box{
        position: relative;
        width: 200px;
        height: 200px;
        border:1px solid red;
    }
    .test{
        position: absolute;
        left: 50%;
        top: 50%;
        transform: translate(-50%,-50%);
        width: 30px;
        height: 30px;
        border:1px solid black;
    }
</style>