JSFiddle - React, Tailwind, and code Playground

HTML

<div class="wrapper">
  <div class="left">
    menu
  </div>
  <div class="right">
    content
  </div>
</div>

CSS

.wrapper {overflow: hidden;}
.wrapper > div { background: #fff;}
.left {
  width: 25%;
  float: left;
}

.right {
  width: 75%;
  float: left;
}