JSFiddle - React, Tailwind, and code Playground
HTML
<div class="header"></div>CSS
body {
font-family: 'Noto Sans', sans-serif;
margin: 0 auto;
height: 100%;
width: 100%;
}
.header {
height: 100%;
width: 70%;
position:absolute;
border: 1px solid red;
box-sizing:border-box;
}