JSFiddle - React, Tailwind, and code Playground

HTML

<section>
    <article>I fill out all the available space!</article>
    <aside>I'm 50px width!</aside>
    </section>

CSS

body {
    display: table;
    table-layout: fixed;
    width: 100%;
    border-spacing: 0;
    border-collapse: separate;
    margin: 0;
}

section {
    display: table-row;
    padding: 25px;
    background: #eee;
    overflow: hidden;
}

article, aside {
    display: table-cell;
    padding: 5px;
}

article {
    background: #cee;
}

aside {
    width: 50px;
    background: #ece;
}

* {
    box-sizing: border-box;
    -webkit-box-sizing: border-box;
    -moz-box-sizing: border-box;
}