How to use a bootrap class as well as a CSS class - html

Question

How can I use 2 different classes? I have 2 HTML option fields when the user selects repair or another in the first one. Then the second must appear. But also its need a bootstrap class: form-control.
<script>
$(function() {
$("#correctiemaatregelen").on("change", function() {
var select_val = $(this).val();
console.log(select_val);
if (select_val === 'Other') {
$("#leveranciers").removeClass("hidden");
document.getElementById("leveranciers");
}
else if (select_val === 'Repair') {
$("#leveranciers").removeClass("hidden");
document.getElementById("leveranciers");
}
else {
$("#leveranciers").addClass("hidden");
$("#leveranciers").val("");
}
});
});
</script>
Correctie maatregelen:<br>
<select name="correctiemaatregelen" class="form-control" id="correctiemaatregelen" style="width: 300px">
<option value="--Correctie maatregel--">--Correctie maatregel--</option>
<option value="Use">Use</option>
<option value="Repair">Repair</option>
<option value="Return">Return</option>
<option value="Other">Other</option>
</select>
<br>
<select name="leveranciers" id="leveranciers" class="form-control hidden" style="width: 300px">
<?php while ($row4 = mysqli_fetch_assoc($result4)):; ?>
<option value="<?php echo $row4['statusname'];?>"><?php echo $row4['statusname'];?></option>
<?php endwhile;?>
</select>
Is there somebody that can help me with this (simple) problem?

Answer 1

Couldn't you just add another class to the element? If this causes problems you have to overwrite some Bootstrap styles with your own class
$(function() {
$("#correctiemaatregelen").on("change", function() {
var select_val = $(this).val();
console.log(select_val);
if (select_val === "Other") {
$("#leveranciers").removeClass("hidden");
document.getElementById("leveranciers");
}
else if (select_val === "Repair") {
$("#leveranciers").removeClass("hidden");
$('#leveranciers').addClass("YOUR_CUSTOM_CLASS");
}
else {
$("#leveranciers").addClass("hidden");
$("#leveranciers").val("");
}
});
});
<select name="leveranciers" id="leveranciers" class="form-control YOUR_CUSTOM_CLASS hidden" style="width: 300px">
<?php while ($row4 = mysqli_fetch_assoc($result4)):; ?>
<option value="<?php echo $row4['statusname'];?>"><?php echo $row4['statusname'];?></option>
<?php endwhile;?>
</select>