JSFiddle - React, Tailwind, and code Playground

HTML

<div class="left"></div>
    <div class="right"></div>

CSS

.right {
    width:200px;
    height:200px;
    background:red;
    float:right;   
}
.left {
    height:200px;
    width:calc(100% - 200px);
    background:blue;
    float:left;
}