Can't change button or font color.

Good afternoon,
I am having a hard time changing/finding a way to change a button that's included in the Appointments+ plugin. The default for this button is white text with a white button. Obviously text cannot be seen like this. I would greatly appreciate some help on the go around to change this. The direct URL for this if you would like to view it is. http://www.alexandrasmysticalworld.com/get-your-reading