@SlowClay a theme MUST include a style.css file in the root theme folder to be a working theme. There is absolutely zero chance that you will purchase a theme here on ThemeForest that doesn’t include a stylesheet. If you are getting the “stylesheet missing” error, you are doing something wrong and there could be 2 very probable reasons:
You are trying to install an HTML template and not a WordPress theme (ThemeForest doesn’t only sell WordPress themes)
If you are 100% confident you are installing a WP theme, you may be uploading the wrong .zip file (maybe you are trying to upload the whole download package including documentation, psd files etc, instead of the theme itself).
Not with WordPress no - you could still use it as it is intended but will need to know how to set it all up - that’s an admin template so you need to have a website for it to manage.
but I still have a question, how about the pages layouts and what I have done changes of the visual composer it will be effected or not? can I do this step without any worries?
Just got the error with x the theme which i downloaded all files including documentation and extracted the x.zip from it and then uploaded as explained in the link you provide but the error came anyway.