让CSS里div上下左右绝对居中几种方式

 1 <div class="box"></div>
 2 #css
 3 .box{
 4 position:absolute/fixed;
 5 left:0;
 6 right:0;
 7 top:0;
 8 bottom:0;
 9 margin:auto;
10 }

 1 <div class="box"></div>
 2 #css
 3 .box{
 4 width:200px;
 5 height: 200px;
 6 position: absolute;
 7 left:50%;
 8 top:50%;
 9 margin-left:-100px;
10 margin-top:-100px;
11 }

1 <div class="box"></div>
2 #css
3 .box{
4 position: absolute;
5 left:50%;
6 top:50%;
7 transform: translate(-50%, -50%);
8 }

1 <div class="box">
2 <div class="child">child</div>
3 </div>
4 #css
5 .box{
6 display:flex;
7 align-items:center;
8 justify-content:center;
9 }

<div class="box">
<div class="child">child</div>
</div>
#css
.box{
display: table-cell;
vertical-align: middle;
text-align: center;
}