JSFiddle - React, Tailwind, and code Playground

HTML

<div id="main">
  <div id="whiteboard">
    <div id="whiteboardPanel">
      <div id="whiteboardContent">
        <span>Blah, blah, ...</span>
      </div>
    </div>
    <div>Some buttons here</div>
  </div>
</div>

CSS

#main {
  height: 100vh;
  display: flex;
}

#whiteboard {
  flex: 1;
  display: flex;
  flex-direction: column;
  background-color: LightGreen;
}

#whiteboardPanel {
  min-height: 0;
  display: flex;
}

#whiteboardContent {
  overflow: auto;
  width: 100px;
  background-color: White;
  display: flex;
}

#whiteboardContent > span {
  height: 1000px;
}

body {
  margin: 0;
}