JSFiddle - React, Tailwind, and code Playground

HTML

<div class="main">
    <div class="aside">
        <div class="aside-inner"></div>
    </div>
    <div class="article">
        <div class="article-inner"></div>
    </div>
</div>

CSS

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

.main {
    display: flex;
    min-height: 100%;
}

.article {
    display: flex;
    flex-grow: 1;
}

.aside {
    width: 30%;
    
    background: #fbfbfb;
}

.aside-inner {    
    width: 200px;
    min-height: 300px;
    
    float: right;
    
    background: #ccc;
}

.article {    
    border-left: 1px solid #c2c2c2;
    background: #ddd;
}

.article-inner {
    width: 300px;
    
    margin-left: 40px;
    
    background: #ccc;
}