[Improvement] : NavBar is Quite Dim thus not visible in dark Theme

[Blacksujit]

Improvement:

1.) The Navbar on the User Interface is Quite dim

2.) For the better visibility and user experience enhancement visual effects or color gradiation can be added in the navbar

Video:

https://github.com/mapillary/OpenSfM/assets/148805811/31f456a9-ed4e-43cb-b208-86853a5ed4e8