JSFiddle - React, Tailwind, and code Playground

HTML

<div class="promoBlock ">
                <div class="promoImg">
                    fixed content 300px
                </div>
                <div class="promoContent">
                    fluid content
                </div>   
             </div>

CSS

.promoBlock { width:90%; margin:auto; } 
.promoImg { width:300px; float:left; background-color:red; }
.promoContent { margin-left:300px; background-color:green; }