JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
  <div id="content"></div>
  <div id="close-button"></div>
</div>

CSS

#container {
  width: 50%;
}

#content {
  width: 100%;
  height: 50px;
  background-color: gray;
}

#close-button {
  float: right;
  margin-left: 100%;
  height: 50px;
  width: 50px;
  background-color: red;
}