Where Can I find My old Custom CSS?

I visited a passive site of mine to obtain some custom coding I did awhile back, before the updates that changed where you added css. On going to “Additional CSS” it was totally blank. Where can I locate my previous coding? I know it must be there somewhere as the particular coding I am looking for is still working on this site. Thanks

You hardcoded it into the headers.php file maybe? Or maybe the theme has another section on its customizer like “Custom Style”?