JSFiddle - React, Tailwind, and code Playground

HTML

<div class="flex">
    <div class="sibling-1">text<br>text<br>text<br>text<br>text<br>text<br></div>
    <div class="sibling-2">text<br>text<br>text<br>text<br>text<br>text<br>text<br>text<br>text<br>text<br>text<br>text<br>text<br></div>
</div>

CSS

.flex {
  display: flex;
  width: 200px;
  position: relative;
}

.flex > div {
   flex: 0 0 50%;
    border: 1px solid black;
    box-sizing: border-box;
}

.sibling-2 {
  position: absolute;
  left: 50%;
  top: 0;
  bottom: 0;
  right: 0;
  overflow: auto;
  
}