JSFiddle - React, Tailwind, and code Playground

HTML

<h1>Centering with button</h1>
<button class="parent">
     <div class="child">
         PINK SQUARE SHOULD BE CENTERED.
         BOTH VERTICALLY AND HORIZONTALLY
    </div>
</button>

CSS

h1 {   font: 13px Verdana;    }

.parent {
   background: linen;
   width: 300px;  
   height: 300px;  
   border: 0px;
}

.child {
    background: pink;  
    width: 200px; 
    height: 200px;
    margin: 0 auto;
    text-align: left;
}