error missing stylesheet css file can’t upload zip file to wordpress via hosting site’s cpanel wordpress toolkit (old werkstatt single use licence, support expired)
Almost certainly you are trying to upload the wrong folder - make sure you are using only the theme folder and not the entire download
Make sure you select the “Installable WordPress file only” option. If you select “All files & documentation”, you will not be able to install this zip as is. Instead unzip the file and then locate the installable theme file within it. Luckily most developers clearly label their files, so it should be pretty easy to find.
you can check this helpful article stylesheet error