JSFiddle - React, Tailwind, and code Playground

HTML

<div class="wrapper">
  <div class="left">left column with shorter content</div>
  <div class="right">
    <div class="scrollable">dynamic content, height could be more or less than #left</div>
  </div>
</div>

<hr>

<div class="wrapper">
  <div class="left">left column with longer content alksjl alsdjike alidek alsdikk las dfiklwkjl iasdifielkjas d alsdjfi laskdfial asdielaf,.asdf </div>
  <div class="right">
    <div class="scrollable">dynamic content, height could be more or less than #left</div>
  </div>
</div>

CSS

.wrapper {
  display: flex;
  width: 200px;
}

.left,
.right {
  outline: 1px solid red;
  width: 50%;
}

.right {
  position: relative;
}

.scrollable {
  position: absolute;
  left: 0;
  right: 0;
  top: 0;
  bottom: 0;
  overflow: auto;
}