I’m not sure what the rules are for naming conventions, but after fussing with a few plugins that kept breaking the site, or not working, I discovered that the CSS reference to .navbar seems to be too common.
The most recent conflict I found is Memphis Document Library.
If I were to be honest, everyone (them and you) should likely have it named .xxx-navbar distinctly to your product: .mdl-navbar, .graphene-navbar and so on.
Regardless, any way to fix this other than editing css code and disconnecting it from your theme updates?