JSFiddle - React, Tailwind, and code Playground

HTML

<div class="parent">
  <div class="placeholder"></div>
  <div class="child">
    some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br /> some long text
    <br />

  </div>
</div>

CSS

.placeholder {
  height: 200vh;
  width: 50%;
  float: right;
}

.child {
  position: fixed;
  top: 0;
  bottom: 0;
  height: 100%;
  overflow-y: auto;
}