JSFiddle - React, Tailwind, and code Playground

HTML

<form action="">
  <input 
  id="icons_txt" 
  type="text" 
  name="icon" 
  required
  title="National Insurance Number is not in the correct format"
  value=""
  pattern="^(?!BG)(?!GB)(?!NK)(?!KN)(?!TN)(?!NT)(?!ZZ)(?:[A-CEGHJ-PR-TW-Z][A-CEGHJ-NPR-TW-Z])(?:\s*\d\s*){6}([A-D]|\s)$"/>
  <input type="submit" class="submit">
</form>

CSS

input[type="text"] {
  padding: 10px;
  display: inline-block;
  width: 200px;
  text-transform: uppercase;
}

form {
  margin: 20px;
}