JSFiddle - React, Tailwind, and code Playground

HTML

<div class="fixedwidth">
<div class="fullwidth"> </div>
</div>

CSS

.fixedwidth {
	background-color:#F00; 
	width:940px; 
	height:450px; 
	margin:0 auto; 
	overflow:visible;
}
.fullwidth {
	background-color:#000; 
	width:100%; 
	height:100px; 
	position:relative; 
	z-index:999;
}