子类在父类居中

//上下左右，都居中 
.box{
             100px;
            height: 100px;
            border: 1px solid blue;
            display: flex;
        }
        .box1{
             50px;
            height: 50px;
            border: 1px solid red;
            margin: auto;
        }

//左右居中 
.box{
             100px;
            height: 100px;
            border: 1px solid blue;
           /*display: flex;*/
        }
        .box1{
             50px;
            height: 50px;
            border: 1px solid red;
            margin: auto;
        }