CSS实现弹性盒子保持水平和垂直居中

弹性盒子

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<style>
  .outer{
    width: 400px;
    height: 400px;
    background-color: antiquewhite;
    display: flex; /*弹性盒子模型*/
    justify-content: center;/*水平居中*/
    align-items: center;/*垂直居中*/
  }
  .inner{
    width: 100px;
    height: 100px;
    background-color: aqua;
    text-align: center;/*文字水平居中*/
    line-height: 100px;/*文字垂直水平居中和高度保持一致*/
  }
</style>
<body>
  <div class="outer">
    <div class="inner">1</div>
    <div class="inner">2</div>
    <div class="inner">3</div>
  </div>
</body>
</html>

结果如下