The missing style.css error
Don't worry, you're just uploading the wrong file
Make sure you’re uploading the <themename>.zip file, not the <themename>_package.zip file. Uploading the download package will result in the following error message:
“The package could not be installed. The theme is missing the style.css stylesheet.”
The theme is not missing the style.css stylesheet, you’re just uploading the wrong file. More on how to correctly upload and install a WordPress theme: Installing a theme.