JSFiddle - React, Tailwind, and code Playground

HTML

<div class="main">
  <div class="son1"></div>
  <div class="son"></div>
</div>

CSS

.main {display: flex;}
.son {flex-grow: 2; height: 50px; background: green;}
.son1 {flex-grow: 1; height: 50px; background: black;}