JSFiddle - React, Tailwind, and code Playground

HTML

<div id="mainpage">
    content
</div>

CSS

body, html {
    height: 100%;
    margin: 0;
    padding: 0;
}
#mainpage
{
    position:relative;
    width:850px;
    margin:0 auto;
    height:70%;
    top:0;
    background: lightblue;
}