I was trying to get the 'Add to Cart' button text to show in #fff through goodstore-child/style.css, but it just don't bite. It adamantly stuck in the custom-styles-1.css. The thing is, the background and the font color are very close (dark grey), there's no contrast at all. So I suppose this is a CSS error in version 1.6.
I've no choice but to change the color to #fff in custom-styles-1.css. Hopefully in the next update, I can remember to change it again.