.wp-block-button__link {
  background: #f27d42;
  border: 0;
  color: #FFFFFF;
  font-family: "Lato" !important;
}
  .wp-block-button__link:hover, .wp-block-button__link:focus {
    background: #022444;
  }

I used this in the tweaks of Robert and it seemed to work really well and allowed to change the button colors if the user wants. 

Obviously, a few of these attributes should be changed once added to the actual theme and depending on the styling of the homepage buttons. #f27d42 change to $secondary or $primary, font-family: $main. #022444 change to other than the first one. I don't know where to add this, but like the button styling file. and just test to make sure that the text color and the background color can be changed.

https://joseph.diocesanweb.org/faith-formation/ I have added things in the tweaks, so you may need to turn those off to test it.