Theme is missing the style.css stylesheet error

Updated: August 18, 2016

With themes purchased from Themeforest portal you may have problems to install theme with downloaded package. Problem is with package that you are trying to upload. It’s probably not zip package with theme files only, but package that include also documentation and licenses from Themeforest.
Zip file with theme itself you can find inside downloaded main zip package.
Follow please official article from Themeforest to resolve issue and find zip file with theme itself: https://help.market.envato.com/hc/en-us/articles/202821510-Theme-is-missing-the-style-css-stylesheet