Quin, I had the same issue with needing the button background to be solid following the update to 1.3.8.1. Figured out how to do this by adding code to Additional CSS section in the Customizer. You’ll probably need to change both the button styling and the hover/focus styling. Here’s an example of what I did:
#agama_slider .slide-1 a.button {
background-color: #439336;
border-color: #439336;
color: white !important;
}
#agama_slider .slide-1 a.button:hover, a.button:focus {
background-color: #fff !important;
border-color: #fff !important;
color: #439336 !important;
}
Hope this helps!