JSFiddle - React, Tailwind, and code Playground

HTML

<div class="cf-full">
    <input id="a" type="text" />
    <label class="helptext">label</label>
</div>

CSS

div {
    display:table;
}
input {
    display:table-footer-group;
}
label {
    display:table-header-group;
}