JSFiddle - React, Tailwind, and code Playground

HTML

<div class="left">
Left
</div><div class="right">
Right
</div>

CSS

.left{
  background-color:red;
  display:inline-block;
  width:100px;
}

.right{
  background-color:green;
  display:inline-block;
  width:calc(100% - 100px);
}