JSFiddle - React, Tailwind, and code Playground

HTML

<form method="post" action="receive.js">
    <input type="text" name="someValue" pattern="[0-9][A-Z]{3}" placeholder="Enter 1 number & 3 uppercase characters" />

    <input type="submit" value="submit" />

</form>

CSS

input[type="text"]{ width: 300px; }