The page element is vertically and horizontally centered, realizing the vertical and horizontal centering of known or unknown width.

Page elements centered vertically and horizontally 、 Vertical horizontal centering of known or unknown width

// 1
.wrapper {
    
  position: relative;
  .box {
    
    position: absolute;
    top: 50%;
    left: 50%;
    width: 100px;
    height: 100px;
    margin: -50px 0 0 -50px;
  }
}

// 2  What I use most 
.wrapper {
    
  position: relative;
  .box {
    
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
  }
}
//  pseudo-classes +vertical-align: middle;
    .box{
        
        vertical-align: middle;
        display: inline-block;
    }
    .wrapper::after{
    
        content: ''; 
        height: 100%; 
        width: 0;  
        vertical-align: middle; 
        display: inline-block;          
    }
// 3
.wrapper {
    
  .box {
    
    display: flex;
    justify-content:center;
    align-items: center;
    height: 100px;
  }


// 4
.wrapper {
    
  display: table;
  .box {
    
    display: table-cell;
    vertical-align: middle;
  }
}