Where do I put this code? Do I use Elements, or a plugin like Code Snippets?
I am hoping that eventually the GenerateBlocks button styles will integrate with the GP customizer to make this easier!
TLDR: Are you using a Child Theme?
If Yes, then you can add that code to your Child Themes functions.php
If No, then use the Code Snippets plugin and add it to a New Snippet.
I am not using a child theme, so I installed Code Snippets. I have set the button background to be a reddish color in the customizer, but it’s still showing the blue background which appears to be the GenerateBlocks default for buttons in a group.