A part of a flexdashboard is permanently in "Dark Mode" while the entire dashboard is in "Light Mode". How can I change it?

Question

Maybe it's something very easy to solve, but I haven't found the problem yet.

I started to develop a Dashboard in Rmarkdown, Flexdashboard and Shiny. At some point I tried the dark theme and it seems that the navigation bar is in dark mode always, and everything else is in "light" mode, since I see it in purple color, and it seems to me that it should be orange.

I attach a reference image.

I am using the "United" theme: https://bootswatch.com/united/

Here is the YAML header:

Does anyone know how to fix it? I don't see where the problem is.

I remain attentive, best regards.