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,
.main, 
.aside, 
.article {
    height: 100%;
    margin: 0;
}

.main {
    display: table;
    border-collapse: collapse;
    
    width: 100%;
    
    -moz-box-sizing: border-box;    
    box-sizing: border-box;    
}

.aside,
.article {
    display: table-cell;
    vertical-align: top;
}

.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;
    min-height: 100%;
    
    margin-left: 40px;
    
    background: #ccc;
}