<select class="selectpicker">
<option>Mustard</option>
<option>Ketchup</option>
<option>Barbecue</option>
</select>
$(function () {
$('select').selectpicker();
});
// To style only selects with the my-select class
$('.my-select').selectpicker();
// To style all selects
$('select').selectpicker();
<!-- Latest compiled and minified CSS -->
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap-select@1.13.14/dist/css/bootstrap-select.min.css">
<!-- Latest compiled and minified JavaScript -->
<script src="https://cdn.jsdelivr.net/npm/bootstrap-select@1.13.14/dist/js/bootstrap-select.min.js"></script>
<!-- (Optional) Latest compiled and minified JavaScript translation files -->
<script src="https://cdn.jsdelivr.net/npm/bootstrap-select@1.13.14/dist/js/i18n/defaults-*.min.js"></script>