css垂直居中的四种方法

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>垂直居中</title>
    <style>
    .parent{ 400px;height: 400px;border:1px solid grey;display: }
    .children{ 200px;height: 200px;background-color: #ccc;}
    /*table-cell*/
    .parent{display: table-cell;text-align: center;vertical-align: middle;}
    .children{display: inline-block;}
    /*flex*/
    .parent{display: flex;justify-content: center;align-items: center;}
    /*position transform*/
    .parent{position: relative;}
    .children{position: absolute;top:50%;left: 50%;transform:translate(-50%,-50%);}
    /*position margin 不推荐使用，使用必须设置宽高*/
    .parent{position: relative;}
    .children{position: absolute;top:0;left: 0;bottom: 0;right: 0;margin: auto;}
</style>
</head>
<body>
    <div class="parent" >
        <div class="children">
        </div>
    </div>
</body>
</html>