JSFiddle - React, Tailwind, and code Playground

HTML

<div class="left-column"></div>

<div class="top-bar"></div>

CSS

.page-wrapper, html, body {
    width:100%;
    height:100%;
    margin:0;
    padding:0;
}

.left-column {
    position:fixed;
    top:0;
    left:0;
    z-index:1000;
    width:250px;
    height:100%;
    background:#090909;
}

.top-bar {
    position:fixed;
    top:0;
    left:250px;
    width:100%;
    height:54px;
    background:yellow;
    z-index:1000;
}