<form action="post" id="number__form">
<input required maxlength="4" type="text" class="card-number__input">
<input required maxlength="4" type="text" class="card-number__input">
<input required maxlength="4" type="text" class="card-number__input">
<input required maxlength="4" type="text" class="card-number__input">
</form>