JSFiddle - React, Tailwind, and code Playground

HTML

<div>
    <div id="left">
        left can be changed and so the div will change
    </div>
    <div id="right">
        right
    </div>
</div>

CSS

#left {
  float: left;
  background-color: red;
}

#right {
  background-color: yellow;
  flex-grow: 1
}