实现效果：

【CSS】一个DIV在另一个DIV上下左右居中（示例）_前端

代码：

<!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>
  </head>

  <style>
    .box1 {
      width: 300px;
      height: 300px;
      background-color: rgb(209, 233, 209);
    }
    .box2 {
      width: 150px;
      height: 150px;
      background-color: rgb(245, 196, 169);
      position: relative;
      margin: 0 auto;
      top: 50%;
      -webkit-transform: translateY(-50%);
      -ms-transform: translateY(-50%);
      transform: translateY(-50%);

      /* 文字居中 */
      text-align: center;
      line-height: 145px;
    }
  </style>

  <body>
    <div class="box1">
      <div class="box2">居中了</div>
    </div>
  </body>
</html>