css实现垂直水平居中的5种方法

给父元素设置table-cell,text-align,vertical-align

#big{
         200px;
        height: 200px;
        border:1px solid #000;
        display: table-cell;
        text-align: center;
        vertical-align: middle;
    }
    #small{
        display: inline-block;
         50px;
        height: 50px;
        background: yellow;
        vertical-align:middle;
    }

给子元素设置margin:auto

#big{
         200px;
        height: 200px;
        border:1px solid #000;
        position: relative;
    }
    #small{
        display: inline-block;
         50px;
        height: 50px;
        background: yellow;
        position: absolute;
        left:0;
        right:0;
        top:0;
        bottom:0;
        margin:auto;
    }

弹性盒

#big{
         200px;
        height: 200px;
        border:1px solid #000;
        display: flex;
        align-items: center;
        justify-content: center;
    }
    #small{
        display: inline-block;
         50px;
        height: 50px;
        background: yellow;
    }

利用translate实现，先进行绝对定位，然后通过translate让它自身往回移动50%

#big{
         200px;
        height: 200px;
        border:1px solid #000;
        position: relative;
    }
    #small{
        display: inline-block;
         50px;
        height: 50px;
        background: yellow;
        position:absolute;
        top:50%;
        left:50%;
        transform:translate(-50%,-50%);
    }

通过新创建一个元素，设置高为父元素的高，让div以这个元素来执行vertical-align

#big{
         200px;
        height: 200px;
        border:1px solid #000;
        text-align: center;
    }
    #small{
        display: inline-block;
         50px;
        height: 50px;
        background: yellow;
        vertical-align: middle;
    }
    span{
        display: inline-block;
         0;
        height: 100%;
        background: red;
        vertical-align: middle; 
    }
    </style>
</head>
<body>
    <div id="big">
        <div id="small">
        </div>
        <span></span>
    </div>
</body>