css实现盒子水平垂直居中--3种常用方法

.box {
        background: red;
        width: 200px; 
        height: 200px;
        position: absolute;
        top: 50%;
        left: 50%;
        margin-top: -100px;
        margin-left: -100px;
    }

.box {
        background: red;
        width: 200px; 
        height: 200px;
        position: absolute;
        top: 0;
　　　　 bottom: 0;
        left: 0;
　　　　 right: 0;
        margin: auto;
    }

.box {
        background: red;
        position: absolute;
        top: 50%;
        left: 50%;
        transform: translate(-50%, -50%);
    }

 <div class="fa">
        <div class="box">我要居中显示</div>
 </div>

 .fa{
        height: 300px;
        display: flex;
        justify-content: center;
        align-items: center;
        margin: 0;
        padding: 0;
    }
    .box {
        background: red;
        width: 200px; 
        height: 200px;
}