CSS 实现垂直居中的5种方法

方法1：使用绝对定位和负外边距对块级元素进行垂直居中

            优点：兼容不错。缺点：必须提前知道被居中块级元素的尺寸

       .father {
            width: 300px;
            height: 300px;
            background-color: red;
            position: relative;
            margin-bottom: 10px;
        }

        #child1 {
            width: 100px;
            height: 100px;
            position: absolute;
            top: 50%;
            left: 50%;
            margin-left: -50px;
            margin-top: -50px;
            background-color: green;
        }

    <div class="father">
        <div id="child1"></div>
    </div>　

方法2：使用绝对定位和transform

            优点：不必提前知道被居中的元素的尺寸

        .father {
            width: 300px;
            height: 300px;
            background-color: red;
            position: relative;
            margin-bottom: 10px;
        }
        #child2 {
            position: absolute;
            top: 50%;
            transform: translateY(-50%);
            background-color: green;
        }

<div class="father">
        <div id="child2">内容撑开</div>
    </div>

方法3：绝对定位结合margin:auto

        .father {
            width: 300px;
            height: 300px;
            background-color: red;
            position: relative;
            margin-bottom: 10px;
        }
        #child3 {
            position: absolute;
            height: 100px;
            width: 100px;
            top: 0;
            bottom: 0;
            left: 0;
            right: 0;
            margin: auto;
            background-color: green;
        }

    <div class="father">
        <div id="child3">内容撑开</div>
    </div>

方法4：flex布局

        #father1 {
            width: 300px;
            height: 300px;
            background-color: red;
            display: flex;
            justify-content: center;
            align-items: center;
        }

        #child4 {
            /* width:100px; */
            width: calc(50% + 1px);
            height: 100px;
            background-color: green;
        }

    <div id="father1">
        <div id="child4">123</div>
    </div>

方法5：用table实现

        #father2 {
            width: 300px;
            height: 300px;
            display: table;
            background-color: red;
        }

        #child5 {
            display: table-cell;
            text-align: center;
            /* 水平居中 */
            vertical-align: middle;
            /* 垂直居中*/
        }

    <div id="father2">
        <div id="child5">内容</div>
    </div>