SOLVED: FF57: Change Google's background color?

[Flycaster]

Installed the revised code and got interesting results. It is the only code residing in userContent.css. When YT opened, the background color was changed to the lavender background...but only momentarily, and then quickly reverted to its original background color-white. However, there now was a definite line that defined the bottom edge of the tab toolbar. Thus, at least, there was now some indication of separation between the website and the tab toolbar???

EDIT: I disabled ColorfulTabs. Only changes were:
1. Google Background...Code still working on Google background (Lavender)
2. YT Background...Remained white and separating line still there
3. Tab toolbar Background...now a dark gray.
4. Tabs...Active tab now white as are the Bookmark and Navigation toolbars. Tabs not in use are now same color as the tab toolbar.