为什么vertical-align不生效呢

为什么vertical-align不生效呢？求解为什么没有垂直居中

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回答：需要将父元素设置一下行高：可以参考这篇文章：https://blog.csdn.net/qq_43677117/article/details/109475579

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<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .one {
            width: 400px;
            height: 400px;
            background-color: red;
            margin: 0 auto;
            text-align: center;
            line-height: 400px;
        }

        .two {
            width: 300px;
            height: 300px;
            line-height: 300px;
            background-color: green;
            display: inline-block;
            vertical-align: middle;
        }

        .three {
            width: 200px;
            height: 200px;
            background-color: blue;
            display: inline-block;
        }
    </style>
</head>

<body>
    <div class="one">
        <div class="two">
            <div class="three">
            </div>
        </div>
    </div>
</body>

</html>