Where do scrollbars come from?

I would like to know where default scrollbars come from and what activates them or deactivates them.

Overnight, the ‘Dewdrop Scrollbar’ plugin disappeared from my site. Someone deleted it, not me. When I reinstalled it, there were no scrollbars at all on my site. I have tried about 8 ways to see how this was happening, uploading old backups, etc., and I can’t pin it down.

All I know is that the site continues to have no scrollbars, so no pages are viewable, and I can’t get any work done. Somebody with skill deleted my Dewdrop plugin and then killed my scrollbars. I wish I knew what to look for to solve the problem.

Thanks in advance for any ideas.

The site is in development, I can’t take maintenance off it just yet.