Hello,

Actually, the Add to Cart and Select Options both are basically the Add to Cart buttons with a slight text and functionality change difference because of the Simple and Variable Product types, which is why our applied CSS is working on both of them.

After thorough checking, we have come to find a specific class for the Select Options button so could you please share your Site WP-ADMIN Login details in the Private Content field so that we can check this concern on your Site and help you out accordingly.

Best Regards