I couldn't get past 'The Problem' because it omits the simplest solution which would be to rename '.button--facebook' to '.button.button--facebook'.
In fact, you could then remove the duplicate 'color: #fff' declaration.
Furthermore, I'd redeclare '.button--ghost' as '.button.button--ghost'. In some editors, like Visual Studio, when you place rules in order and press CTRL+K+D, it will indent them in the form of a tree.
In fact, you could then remove the duplicate 'color: #fff' declaration.
Furthermore, I'd redeclare '.button--ghost' as '.button.button--ghost'. In some editors, like Visual Studio, when you place rules in order and press CTRL+K+D, it will indent them in the form of a tree.