各种居中

1- 水平居中

inline-block + text-align

    <div class="parent">

        <div class="child">DEMO</div>

    </div>

    .child{

        display: inline-block;

    }

    .parent{

        text-align: center;

    }

table + margin

    .child{

        display: table;

        margin:0 auto;

    }

absolute + transform

    .parent{

        position: relative;

    }

    .child{

        position: absolute;

        left: 50%;

        transform: translateX(-50%);

    }

flex + justify-content

    .parent{

        display: flex;

        justify-content: center;   /*margin: 0 auto; 也可以*/

    }

2-垂直居中

table-cell + vertical-align

.parent{

    display: table-cell;

    vertical-align: middle;

}

absolute + transform(和水平居中的方法一样)

flex + align-items

.parent{

    display: flex;

    align-items: center;

}

3- 水平垂直居中

inline-block + text-align + table-cell + vertical-align

.parent{

    text-align: center;

    display: table-cell;

    vertical-align: middle;

}

.child{

    display: inline-block;

}

absolute + transform

flex + justify-content + align-items