JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
  <div class="column-1">
    column 1
  </div>
  <div class="column-2">
    <div class="item-container">
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
      <div class="item"></div>
    </div>
  </div>
</div>

CSS

.container {
  display: flex;
  flex-direction: row;
  width: 100%;
  height: 100%;
  background: red;
}

.column-1 {
  flex: 50%;
  height: 100%;
  background: lightblue;
}

.column-2 {
  flex: 50%;
  height: 100%;
  background: lightgreen;
}

.item-container {
  width: 100%;
  overflow: auto;
  background-color: rgba(255, 165, 0, 0.6);
}

.item {
  width: 500px;
  height: 20px;
  background: orange;
}

html, body {
  height: 100%;
}