使div在背景图像div内居中

<style>
  .background {
    display: flex;
    justify-content: center;
    align-items: center;
  }
</style>

<div class="background">
  <div>要居中的内容</div>
</div>

<style>
  .background {
    position: relative;
  }

  .centered {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
  }
</style>

<div class="background">
  <div class="centered">要居中的内容</div>
</div>