Is there a way to change the color of a dropdown menu via CSS in flexdashboard?

Question

I am writing a flexdashboard and I would like to change its colors.

I've managed to get somewhat what I want with this css:

<style>
body {
  padding-top: 50px;
}
.section.sidebar {
  top: 51px;
  background-color: rgba(76, 18, 17, 0.95);
  color: #ffffff
}
.value-box {
  color: #ffffff;
}
.navbar {
  background-color: rgba(76, 18, 17, 1);
  border-color: #ffffff
}
.navbar-brand {
  color: #ffffff;
}
.navbar-nav li a:hover, .navbar-nav > .active > a {
  color: rgba(76, 18, 17, 0.8) !important;
  background-color: #ffffff !important;
  background-image: none !important;
}
.dropdown-toggle li a {
  color: rgba(76, 18, 17, 0.8) !important;
  background-color: #ffffff !important;
  background-image: none !important;
}
</style>

I must say that I do not know css. The above code may be redundant or some of its lines can be plain non-sense. I did it by scraping over answers on stack overflow. It gives the following result:

This is basically what I want except for this blue color that appears when I click over a navbar-menu option. How do I change this? It also makes A and B blue when I select them, and I would want to change that.

From what I've read on css on the internet, I came up with the following code:

.dropdown-toggle li a {
  color: rgba(76, 18, 17, 0.8) !important;
  background-color: #ffffff !important;
  background-image: none !important;
}

but this doesn't solve my problem.

Any help is appreciated. If someone could also point me to some reference that covers these things, it would be great.