JSFiddle - React, Tailwind, and code Playground

HTML

Old:
<div id="old">
<h1>Hello world</h1>
    <h1>Hello world</h1>
</div>
New:
<div id="flex">
<h1>Hello world</h1>
    <h1>Hello world</h1>
</div>

CSS

#old {
    display: -webkit-box;
    -webkit-box-pack: center;
    -webkit-box-align: center;
    -webkit-box-orient: vertical;
}
#flex {
    display: -webkit-flex;
    -webkit-justify-content: center;
    -webkit-align-items: center;
    -webkit-flex-direction: column;
}

div {
    background:orange;
    width:200px;
    height:200px;
}