如何在另一个DIV内联显示固定大小的DIV？

<div id="container">
  <div id="fixedDiv"></div>
</div>

#container {
  position: relative;
  width: 500px;
  height: 300px;
  background-color: #f2f2f2;
}

#fixedDiv {
  position: absolute;
  width: 200px;
  height: 100px;
  background-color: #ccc;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}

<style>
  #container {
    position: relative;
    width: 500px;
    height: 300px;
    background-color: #f2f2f2;
  }

  #fixedDiv {
    position: absolute;
    width: 200px;
    height: 100px;
    background-color: #ccc;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
  }
</style>

<div id="container">
  <div id="fixedDiv"></div>
</div>