Resolve 'UnityEditor' error

Happy New Year everyone.

Help me with this question, I have the DayNightGradient package which is having an error when im building my project.

It says the type or namespace name UnityEditor could not be found.

I know that types like this must be on Editors folder
But if i move that script to Editors folder, the references and many things goes wrong

So I need a resolution for this an in easiest way.
Please help me out on this on, this is a long story with this problem.

If you need, the link to DayNightCycle project is here:
GitHub link

Editor scripts are for use in the editor only. Nothing editor related will end up packaged in the build, so if you have actual game code dependent on an editor script, you need to refactor that code. Editor scripting is only to help you get the object set up. Not to actually do anything at run time. Even if you managed to get everything straightened out with putting it into an editor folder, it wouldn’t be included in the actual build.

-Larry