Removing default button

I’m using this code to remove the default button, but it sometimes causes a “headers already sent” error. Is there a better way to accomplish the same task?

function seamless_donations_cmb2_remove_primary_save_button() {
     ?>
     <style type="text/css" media="screen">
         input#submit-cmb.button.button-primary {display: none;}
     </style>
     <?php
}