JSFiddle - React, Tailwind, and code Playground

HTML

<form>
    <fieldset>
        <legend>A form</legend>
        <label for="text">A label</label>
        <input id="text" placeholder="A text input" />
    </fieldset>
    <div>
        <button>Button A</button>
        <button>Button B</button>
    </div>
    <fieldset class="flex">
        <button>Button A</button>
        <button>Button B</button>
    </fieldset>
</form>

CSS

form>fieldset:not(:last-of-type) {
    display:flex;
    flex-direction: column;
}
form>fieldset:not(:last-of-type)>input {
    width: 100%;
}
div, fieldset.flex {
    display: -webkit-flex;
	display: flex;
    -webkit-flex-direction: row;
    flex-direction: row;
    -webkit-justify-content: center;
    justify-content: center;
}