JSFiddle - React, Tailwind, and code Playground

HTML

<h1>Centering Content</h1>
<div id="outer">
    <div id="blueDiv"></div>
    <div id="redDiv"></div>
</div>

CSS

#outer {
  width: 200px;
  height: 400px;
  background-color: #333333;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
}
h1 {
    font-family: "Franklin Gothic Medium", sans-serif;
    font-size: xx-large;
    color: #3399FF;
}
#blueDiv {
    width: 100px;
    height: 100px;
    background-color: #3399FF;
}
#redDiv {
    width: 100px;
    height: 100px;
    background-color: red;
}