The OverlayScrollbars website links to the MIT wikipedia page but I don't see a license file anywhere in the repo or on the website. Can you add a LICENSE.txt for MIT? (or whichever license you prefer)
This might help: https://help.github.com/en/articles/licensing-a-repository
You might thought that this repo is the plugins repo, but its just the repo for the Github-page. The OverlayScrollbars Github repo has a LICENSE file for each provided package.
The OverlayScrollbars website links to the MIT wikipedia page but I don't see a license file anywhere in the repo or on the website. Can you add a LICENSE.txt for MIT? (or whichever license you prefer) This might help: https://help.github.com/en/articles/licensing-a-repository