JSFiddle - React, Tailwind, and code Playground

HTML

<div id="parent">
  <div id="header"></div>
  <div id="content"></div>
</div>

CSS

#parent {
  background: teal;
  height: 200px;
}

#header {
  background: coral;
  height: 40px;
}

#content {
  background: #eee;
  max-height: calc(100% - 40px); /* 100% - height of header */
  overflow-y: auto
}