A common issue that can occur with users new to installing WordPress themes is a “Broken theme and/or stylesheets missing” error message being displayed when trying to upload or activate the theme. This error message does not mean that the theme you have purchased is broken, it simply means it has been uploaded incorrectly. Luckily, there is a very easy fix.
One of the reasons you may receive this error is if you have uploaded the incorrect file. You have 2 options for downloading your theme.
1. Installable WordPress file only.
2. All files and documentation (full zip folder). You will need to extract and locate the installable WordPress file.
SOLUTION: Please make sure you are uploading only the installable theme which is called NameOf Theme.zip. If you upload ALL these files you will receive an error.
Read more here.