Some people reported that in some levels the background was the wrong size and it was possible to see a gap in the sides with a different color.
The background has been adjusted and now the problem has been fixed.
Background size
Source: Steam Community (opens in a new tab)
Build and release context
Steam update times within 24 hours of this post. Matching dates do not confirm which build it describes.
Build 9473267 · public branch
Steam updated · First observed