JSFiddle - React, Tailwind, and code Playground

HTML

<header>topo</header>
<aside>menu</aside>
<div>conteĂşdo</div>

CSS

* { margin: 0; padding: 0 }
html, body { height: 100% }

header, aside, div {
    display: inline-block
}

header {
    background-color: #7396FF;
    height: 50px;
    width: 100%
}

aside {
    background-color: #FF4D4D;
    height: 100%;
    width: 30%;
}

div {
    background-color: #FFDC73;
    float: right;
    height: 100%;
    width: 70%;
}