JSFiddle - React, Tailwind, and code Playground

HTML

Reservation <br/>
<select id="rReservation" name="rReservation" class="">
                                <option value="0">Maybe</option>
                                <option value="1">Sure</option>
</select>
<hr/>
Name <br/>
<input type="text" name="rCardUser" class="mRequired" />

<hr/>
Card<br/>
<input type="text" name="rCardNrr" class="mRequired" />

CSS

.required {
 border: 1px solid red;   
}

JavaScript

if ($("#rReservation").val() == "1") {
   $('.mRequired').addClass('required');
} else {
   $('.mRequired').removeClass('required');
}