A common issue that can occur when installing a WordPress themes is “The package could not be installed. The theme is missing the style.css stylesheet.” error message being displayed when uploading or activating the theme.
The downloaded theme package may consist of actual theme along with documentation, plugins, and some other stuff.
To avoid this error you must unzip/unpack the downloaded theme package, thereafter find the theme installation .zip file inside the package and use it for installation in WordPress.
Using Download Manager
We do not recommend the use of download managers to download the files from GETALLGPL.
Download managers send multiple requests and create multiple connections to the server – each one counting as a download. The server will receive an abnormally large amount of requests to download the file(s) and may result in errors.