css多种方法实现已知宽度和未知宽度的元素水平垂直居中

// html

<div class="box-wrapper">
    <div class="box">
        内部box
        <p>更多内容</p>
    </div>
</div>

//css

.box-wrapper{

    width: 100%;
    height: 300px;
    border: 1px solid #f00;
    .box{
       background-color: #0f0;
    }

}

1、已知box宽高

.box-wrapper{
    position: relative;
    
    .box{
         position: absolute;
         top: 50%;
         left: 50%;
         width: 200px;
         height: 100px;
         margin-top: -50px;
         margin-left: -100px;
    }
}

2、未知box宽高

.box-wrapper{
    position: relative;
    .box{
         position: absolute;
         top: 50%;
         left: 50%;
         transform: translate(-50%, -50%);
    }
}

3、未知box宽高

.box-wrapper{
    display: flex;
    justify-content: center;
    align-items: center;
}

4、未知box宽高, 内容垂直居中

.box-wrapper {
  display: table-cell;
  vertical-align: middle;
  width: 400px;
  text-align: center;
  .box{
      display: inline-block;
   }

}