I see. If you’re using GB Pro, you can use Global Styles for all GB Buttons. Reference: https://docs.generateblocks.com/article/global-styles
Otherwise, you can try adding this through Appearance > Customize > Additional CSS:
a[class*="button"] {
background-color: #8f0c51 !important;
padding: 10px 30px 10px 30px !important;
}
This code targets all links with a class that has button text.
You may alter the values in this code to your preference.