垂直居中

方案一 table-cell vertical-align

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>垂直居中 table-cell vertical-align</title> 
    <link rel="stylesheet" type="text/css" href="../../reset.css">
    <style type="text/css">
    .parent{
        background: #bebebe;
        width: 50px;
        height: 200px;
        


        display: table-cell;/* 子元素child就变成了一个单元格 */
        vertical-align: middle;/* 子元素垂直居中 */
    }
    .child{
        background: #404040;
        color:white;
        width: 50px;
        height: 50px;
    }
    </style>
</head>
<body>
<div class="parent">
    <div class="child">DEMO</div>
</div>
</body>
</html>

方案二垂直居中absolute_transform

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>垂直居中absolute_transform</title>
    <style type="text/css">
    .parent{
        background: #404040;
        height: 300px;
        width: 50px;

        position: relative;
    }
    .child{
        background: #bebebe;
        height: 50px;
        width: 50px;

        position: absolute;
        top: 50%;
        transform: translateY(-50%);
    }
    </style>
</head>
<body>
<div class="parent">
    <div class="child">DEMO</div>
</div>
</body>
</html>

方案三垂直居中flex_align-items

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>垂直居中flex_align-items</title>
    <style type="text/css">
    .parent{
        background: #bebebe;
        height: 300px;
        width: 50px;

        display: flex;/* 收缩 */
        align-items:center;/* 只设置display:flex时， align-items默认为 stretch 即拉伸，*/

    }
    .child{
        background: #404040;
        /*height: 50px;*/
        width: 50px;
        color: white;
    }
    </style>
</head>
<body>

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

</body>
</html>

垂直居中

方案一 table-cell vertical-align

方案二 垂直居中absolute_transform

方案二垂直居中absolute_transform