JSFiddle - React, Tailwind, and code Playground

HTML

<div>
    <input type="text"/>
    <span><button>button</button></span>
</div>

CSS

div {
    border: 1px solid #000;
    display: table;
    width: 100%;
}

div > * { display: table-cell; }

div > span { width: 1%;  }
div > input { width: 100%; }