Logic X Theme Installation:
Logic X has a 'Resources' Folder where the new theme elements are to be copied to. In order to find the Resources folder - you need to go to the Logic X application and right-click 'show package contents'. Now navigate to the folder:
First of all - please copy a version of your original 'Resources' folder to a safe location on your drive - because you are going to modify the original folder when you make changes.
With a copy safely backed up on your drive - you can now drag or copy the contents of the new theme into your Logic X 'Resources' folder. Please 'replace' and 'apply to all' the components when alerted.
Now open Logic X and you will see the new theme - enjoy!
*Note - you can revert to the old theme by copying your original Resources folder back in if necessary.