JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">empty container</div>

<div class="container">
    <div id="inside_1">inside</div>
</div>

<div class="container">
    <div id="inside_2">inside</div>
</div>

CSS

.container{width:500px;height:50px;background-color:#999;margin:5px;}

#inside_1{width:100%;padding:10px;background-color:red;}

#inside_2{padding:10px;background-color:red;}