Change color of the Navbar and ActionsBar in BigBlueButton

[Larshie]

We are running BigBlueButton Ver. 2.6.15 on a Ubuntu 20.04 server. We need to change the color of the Navbar and the ActionsBar located above and below the central Presentation container on the classroom screen. The current color is dark blue (#06172A). Having searched through all configurations files I still cannot find where in BBB the colors of the Navbar and ActionsBar are defined.

If anyone can give me the name and location of the file(s) that define those colors, I will be most grateful !