Applying a CSS style within PHP code

I'm trying to apply a CSS style within a line of PHP code, but haven't had any luck. Anyone have any suggestions?

This is my line of code:

<?php sc_displayCountryField('billing_country', 'billing_province'); ?>

This is one of my attempts which shows what I'm trying to do:

 <?php sc_displayCountryField('billing_country', 'billing_province', 'class="dropdown-form"'); ?>

Here's another attempt that produced no results:

 <?php 
$sc_displayCountryFields = sc_displayCountryField('billing_country', 'billing_province');
echo '<div class="dropdown-form">' . $sc_displayCountryFields . '</div>';
 ?>

Any suggestions would be appreciated,

Zicky