Open modal window with text link

Hello,
I have searched the topics for this but no solution found on them. Please i need custom css for changing the invoke button into a text link. and where should i go to edit the modal window button. Please, if i can get an example with custom css code then i can handle it myself. Please Dont ask for my site url, it will take time set up another admin and direct you to the exact page. Just an example will do.

thanks