JSFiddle - React, Tailwind, and code Playground

HTML

<html>
  <head>
    <link rel="stylesheet" href="https://design-system.service.gov.uk/stylesheets/main-80dad55624186d1808333b42df42da88.css">
  </head>
  <body>
    <div class="container">
      <fieldset class="govuk-fieldset">
        <legend class="govuk-fieldset__legend govuk-fieldset__legend--xl">
          <h1 class="govuk-fieldset__heading">
            What is your address?
          </h1>
        </legend>
        <div class="govuk-form-group govuk-!-margin-bottom-2">
          <label class="govuk-label" for="address-line-1">
          Building and street
          <span class="govuk-visually-hidden">line 1 of 2</span>
          </label>
          <input class="govuk-input" id="address-line-1" name="address-line-1" type="text">
        </div>
        <div class="govuk-form-group">
          <label class="govuk-label" for="address-line-2">
          <span class="govuk-visually-hidden">Building and street line 2 of 2</span>
          <span class="govuk-hint float-right">(Optional)</span>
          </label>
          <input class="govuk-input" id="address-line-2" name="address-line-2" type="text">
        </div>
        <div class="govuk-form-group">
          <label class="govuk-label" for="address-town">
          Town or city
          </label>
          <input class="govuk-input govuk-!-width-two-thirds" id="address-town" name="address-town" type="text">
        </div>
        <div class="govuk-form-group">
          <label class="govuk-label" for="address-county">
          County
          </label>
          <input class="govuk-input govuk-!-width-two-thirds" id="address-county" name="address-county" type="text">
        </div>
        <div class="govuk-form-group">
          <label class="govuk-label" for="address-postcode">
          Postcode
          </label>
          <input class="govuk-input govuk-input--width-10" id="address-postcode" name="address-postcode" type="text">
        </div>
      </fieldset>
    </div>
  </body>
</html>

CSS

.container {
  padding: 50px;
}

.float-right {
  float: right;
}