JSFiddle - React, Tailwind, and code Playground

HTML

<div id="main">
    <div id="first">
        <div>1</div>
        <div>2</div>
        <div>3</div>
    </div>
</div>

CSS

div#main { border: 2px dashed red; }

div#first {
    border: 1px double black;
    display: flex;
}

div#first > div {
    flex: 1;
    border: 1px solid black;
    text-align: center;
}