Text Overlay

Hey guys, Im looking on adding a text overlay box over the Slider on my site. I have tried the code from this thread: https://catchthemes.com/support-forum/topic/full-frame-pro-front-page-image-slider/ But I couldent get it to work. Do I add this code under "Additional CSS code" in the Customizer? I would like to have a transparent box with the text thats on the main page, so I can keep the main page clean. Thanks for the help!