JSFiddle - React, Tailwind, and code Playground

HTML

<header>topo</header>
<aside>menu

    <span>fim</span>
</aside>
<div>conteĂşdo</div>

CSS

* { margin: 0; padding: 0 }

body {
    position: relative;
    width: 100%;
}
body, header, aside, div {
    display: inline-block
}

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

aside {
    background-color: #FF4D4D;
    position: absolute;
    top: 50px;
    bottom: 0;
    width: 30%;
}
    aside span {
        position: absolute;
        bottom: 0;
        left: 0;
    }

div {
    background-color: #FFDC73;
    float: right;
    height: 1000px;
    width: 70%;
}