JSFiddle - React, Tailwind, and code Playground

HTML

<div class="main-container">
  <div class="content">
    <h1>Some list</h1>
    
    <div class="post-list">

      <div class="post-item"> <div class="test"> 1. some content </div> </div>
      <div class="post-item"> <div class="test"> 2. some content </div> </div>
      <div class="post-item"> <div class="test"> 3. some content </div> </div>
      <div class="post-item"> <div class="test"> 4. some content </div> </div>

    </div>
  </div>
</div>

CSS

html,
body {
  height: 100%;
}

* {
  box-sizing: border-box;
}

.main-container {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  height: 100%;
  background-image: linear-gradient(45deg, #85ffbd 0%, #fffb7d 100%);
}

.content {
  width: 75%;
  max-height: 500px;

  background-color: white;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
}

.post-list {
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;


  background-color: rgba(0, 0, 0, 0.03);
  width: 95%;
  border-radius: 5px;
  overflow-y: scroll;
  overflow-x: hidden;
  position: relative;
}

.post-item {
  border: 1px solid black;
  width: 100%;
  margin: 0.5rem;
}

.test {
  height: 8rem;
  background-color: rgba(255, 0, 0, 0.1);
  width: 100%;
  text-align: center;
}