JSFiddle - React, Tailwind, and code Playground

HTML

<div id='container'>
    <div id='left'></div>
    <div id='sidebar'></div>
</div>

CSS

html, body {
    height:100%;
}
#container{
    position:relative; 
    height:100%;
}
#left {
    position:absolute;
    left:0;
    right:342px;
    height: 100%;
    background:dodgerblue;
}
#sidebar {
    width: 342px;
    height: 100%;
    float:right;
    background:hotpink;
}