2018-02-23T09:09:36Z||2018-02-23T09:09:36Z
把外层div的align-items和justify-content都设置成center就好。
完整的HTML代码：
<html>
<head>
<meta charset="utf-8" />
<meta name="viewport" content="width=device-width, initial-scale=1" />
<title>Title</title>
<style>
.container {
display: flex;
align-items: center;
justify-content: center;
background-color: yellowgreen;
width: 200px;
height: 200px;
}
.child {
background-color: blue;
width: 100px;
height: 100px;
}
</style>
</head>
<body>
<div class="container">
<div class="child"></div>
</div>
</body>
</html>