Changing the generic version of the facebook button css?

Not exactly, but since the facebook login button uses Iframe to make the css (for example the "a friend uses *site*" text), it might be impossible to change that text. I wanted to change the text to white, but it did not work. But this how ever changed the background color of the whole facebook button.

               <div id="signup" class="fb-login-button" data-max-rows="10"
                    style="background-color: rgba(255,255,255,0.5)"
                    data-size="xlarge" data-show-faces="true"
                    data-auto-logout-link="false"
                    onclick="signUpWithFacebook()">
                    Opret med Facebook
                </div>