不确定我是否正确理解了这些条件，但假设目标是在容器内滚动时使#item始终部分可见，也许可以尝试在#item上设置position: sticky。
这样，可以通过top和bottom来指定当#item粘附到边界时#item的偏移范围。
示例：

#body {
  height: 200px;
  overflow: scroll;
  font-family: sans-serif;
  font-size: 40px;
  background-color: rgba(255, 0, 0, 0.1);
}

#container {
  width: 50%;
  margin: 0 auto;
  height: 900px;
  position: relative;
  display: flex;
  flex-direction: column;
  justify-content: center;
}

#item {
  background-color: rgba(0, 0, 255, 0.1);
  padding: 10px 20px;
  border-radius: 5px;
  position: sticky;
  top: -50px;
  bottom: -50px;
}

#spacer {
  height: 220px;
}

<div id="body">
  <div id="container">
    <div id="spacer"></div>
    <div id="item">
      Hello
    </div>
  </div>
</div>

div{
  width:150px;
  height:150px;
  background: purple;
  opacity: .25;
  border-radius:10px;
  margin:auto;
  position:sticky;
  top:-130px;
  bottom:-130px;
}

<p>Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.</p>
<p>Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.</p>
<div></div>
<p>Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.</p>
<p>Lorem Ipsum has been the industry's standard dummy text ever since the 1500s, when an unknown printer took a galley of type and scrambled it to make a type specimen book. It has survived not only five centuries, but also the leap into electronic typesetting, remaining essentially unchanged. It was popularised in the 1960s with the release of Letraset sheets containing Lorem Ipsum passages, and more recently with desktop publishing software like Aldus PageMaker including versions of Lorem Ipsum.</p>

让我知道你的想法。

既然你悬赏了这个，我不能把它标记为重复，所以我只把它作为一个答案：
问题是：Can a position:absolute element be made sticky?
The unappreciated correct answer.
这是我刚刚整理出来的a new answer，这是一个正在进行中的工作，它有可能被采用来解决上面的问题，等待对底层问题的澄清。