Thanks a lot for the response! Unfortunately, I tried it, and it didn’t fix the issue. The developer has a different theory about the problem than I do: he says, “the issue with the white below the slider is because the slider is extending down below the box. i’m not sure why — there is a min height setting, but no max height so it’s not clear how the height is getting set.” He wondered if you had a suggestion about that.
re: link
The site is password-protected, so I can’t post the link, but here’s a link to a screenshot–I added some green arrows pointing out the white-box problem.