Important: If you have an error or white screen after updating Elementor, please see here for the solution: http://bit.ly/2KRhmLQ

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The package could not be installed. The theme is missing the style.css stylesheet.

This is a common error are there are two zips you download from themeforest, a solution to this issue is in this article.

https://help.market.envato.com/hc/en-us/articles/202821510?_ga=1.61327468.1140640435.1445836150

I hope this helps.