Why does error occurs?
Most of the WordPress users commonly gets “style.css missing” issue while installing the theme which is zipped along with other files inside. And this is also one of the mistake that beginners make. Some of the premium WordPress Themes includes some documentation of theme and licensed agreement files in a theme bundle file.So when you download theme , a theme bundle is downloaded along with those files.
How to get ride of this?
After downloading the theme bundle you need to extract it first then you will get actual theme zip file along with documentation of theme and licensed agreement files. That second zip file is the actual file that you need to upload via your WordPress dashboard.
The error “style.css missing” only occurs when you try to directly upload the theme which is bundled with other files along with the theme.