JSFiddle - React, Tailwind, and code Playground

HTML

<div id="contents">
<h1>Willkommen</h1>
  <div id="bookofmonth">
  <h2>Das Buch des Monats</h2>
  </div>
    <br style="clear:both" /
</div>
<div id="contents">

CSS

#contents{
    background-color:red;
    width:400px;
}
#bookofmonth{
    background-color:yellow;
    width:40px;
    height:40px;
    float:right;
}