A common issue that may occur with users new to installing WordPress themes is a “ The package could not be installed. The theme is missing the style.css stylesheet.” error message.
It is always displayed when trying to upload the theme. This is because the theme download package on ThemeForest includes additional files to the theme such as the documentation, license etc.
This is because the theme download package on ThemeForest includes additional files to the theme such as the documentation, license, import files, plugins zip-files etc.
To solve this simply unzip the theme package themeforest-19200310-native-powerful-startup-development-tool.zip archive and install only the inner theme archive.
More details on correct theme installation can be found in this post.
Regards, DFD Support Team