JSFiddle - React, Tailwind, and code Playground

HTML

<body>
    
    <div class="width900">
    Width of 900px
    </div>
    
    <div class="widthfull">
        <div class="text">
          Width of 100%
        </div>    
    </div>
    
    <div class="width900">
    Width of 900px
    </div>
</body>

CSS

body {width:100%;}

.width900 {width:300px; background:#ccc; margin:auto;}
.widthfull {width:100%; background:#eee; margin:auto;}
.widthfull .text {width:300px; margin:auto;}