JSFiddle - React, Tailwind, and code Playground

HTML

<div id="blue">
  I'm blue ! (dabadee dabada)
</div>
<br/><br/>

<div id="body">
  <div id="red">
    I'm red ! James Red.
  </div>
</div>
<br/><br/>

<div id="body2">
  <div id="red2">
    I'm red ! James Red.
  </div>
</div>

CSS

#blue {
  background-color:blue;
  width:100%
  height:100%
}

#body {
  width : 100%;
  border:1px solid green;
}

#red {
  width:100px;
  background-color:red;
}

#body2 {
  width : 100%;
  border:1px solid green;
}

#red2 {
  width:100px;
  background-color:red;
  margin:0 auto;
}