Remove Form Field

I have difficulty removing default fields from the Add Listing front end page. For the website link I have put .form-row-rapper-buy_link {display:none; } in every css file I could find, but the field was still there. I believe the description for that field is generated and I don’t know how to remove the specific field and on which css file I should put it, since the one from admin panel is not used. Thanks for your help.