JSFiddle - React, Tailwind, and code Playground

HTML

<button>1</button>
<button>2<span>2.1</span></button>
<button>3</button>
<button>4</button>
<button>5</button>
<button>6</button>

CSS

button {height:60px;width:50px;border:1px solid #000;box-sizing:border-box}
button span {color:grey; font-size:9px}