I’ve saved the code as given, I’ve doubled checked again.
Kindly check the link below that will direct you to a video of what I am doing. The first part of the video is to show you how I am saving the CSS file. The second segment shows where could I change the theme’s colors using the “Fourteen Colors” plugin; There is no option related to button text color.
https://screencast.com/t/tnfilJiqF