JSFiddle - React, Tailwind, and code Playground

HTML

<div class="wrapper">
		
			<header class="header">
				Menu
			</header>
			<section  class="full-width">
				Content
			</section>
			
		</div>

CSS

body {
			margin: 0;
			background: white;
		}
		.wrapper {
			width:100%;
			margin:auto;
		}
		.header{
			width:200px;
			height: 100%;
			float:left; 
			background-color:#333;
			display: block;
			color: white;
		}
		.full-width {
			margin-left: 200px;
			height: 100%;
			float: none;
			background: #888;
			display: block;
			
		}