JSFiddle - React, Tailwind, and code Playground

HTML

<div class="main">
    <div class="fixed_right">
        Right Column is skinny.
    </div>
    <div class="scaling_left">
        Left column is variably fat.
    </div>

</div>

CSS

.main 
{
    width: 100%;
    overflow: auto;
}

.scaling_left
{
    margin-right: 100px;
    background-color: #D9F2D0;
}
.fixed_right
{
    float:right;
    width: 100px;
    background-color: #efefef;
}