布局-水平垂直居中

结构：

1 <div class="parent">
2         <div class="child">DEMO</div>
3     </div>

样式：

1.解决方案一：text-align + inline-block + table-cell + vertical-align(结合前面的水平居中+垂直居中)

 1 .parent {
 2         background-color: grey;
 3          300px;
 4         height: 200px;
 5 
 6         display: table-cell;
 7         vertical-align: middle;
 8 
 9         text-align: center;
10     }
11     .child  {
12         display: inline-block;
13         background-color: skyblue;
14     }

2.解决方案二： absolute+transform

.parent {
        background-color: grey;
         300px;
        height: 200px;

        position: relative;
    }
    .child  {
        position: absolute;
        top: 50%;/*相对容器的百分比*/
        left: 50%;
        transform: translate(-50%,-50%);/*相对自身的百分比*/
        background-color: skyblue;
    }

3.解决方案三：flex + justify-content + align-items

.parent {
        background-color: grey;
         300px;
        height: 200px;

        display: flex;
        justify-content: center;
        align-items: center;
    }
    .child  {
        
        background-color: skyblue;
    }