@keptfrozen You can add this code snippet within the Custom CSS panel to remove opacity on button hover:
#siteWrapper.site-wrapper .sqs-block-button-element:hover, .sqs-button-element--primary:hover {
opacity: 1 !important;
}
I'm not aware of any class system documentation specifically available for Circle members. You might find this blog post helpful: https://launchhubstudio.com/blog/squarespace-css-selectors