Form radio toggles, sans JS

form.html

<form class="form">
  <legend class="form__headline">Billing Info</legend>

  <fieldset class="form__section">
    <input type="radio" name="payment-method" value="stripe" class="form__section__radio" checked/>
    <label>Credit Card</label>

    <div class="form__section__content">
      <button>Secure checkout</button>
    </div>
  </fieldset>

  <fieldset class="form__section">
    <input type="radio" name="payment-method" value="apple-pay" class="form__section__radio"/>
    <label>Apple Pay</label>

    <div class="form__section__content">
      <button>Secure checkout</button>
    </div>
  </fieldset>

  <fieldset class="form__section">
    <input type="radio" name="payment-method" value="paypal" class="form__section__radio"/>
    <label>PayPal</label>

    <div class="form__section__content">
      <button>Secure checkout</button>
    </div>
  </fieldset>
</form>

form.scss

.form__section__radio {
  // style

  & ~ label {
    // style
  }

  &:not(:checked) {
    // style

    & ~ label ~ .form__section__content {
      margin: 0; padding: 0;

      height: 0;
      opacity: 0;
      visibility: hidden;
    }
  }

  &:checked {
    // style

    & ~ label ~ .form__section__content {
      // add margin/padding that works for you
      opacity: 1;
      visibility: visible;
    }
  }
}