list of css selectors for 2.03 default template?

Hi

Trying to identify the exact css selector for a button in the default template in 2.03.
It's the button that appears in the navbar when collapsed for small screens.

<button type="button" class="btn btn-navbar navbar-toggle" data-toggle="collapse" data-target=".navbar-ex1-collapse"><i class="fa fa-bars"></i></button>

I have tried all combinations and can't get the colour to change.
.btn
.btn-primary
etc.

Can anyone advise the exact selector?
thanks