Creating on behalf of customer: It’s not currently possible to attach a stylesheet to a CTA. Although it's possible to attach a stylesheet to a page or page template, and so style CTAs, those styles aren’t used in the CTA editor itself. It’s thus not possible to preview how a CTA styled by a custom CSS class will look without creating a page and adding the CTA to it (as well as attaching the appropriate stylesheet to the page). While, on one hand, this provides for some amount of flexibility from a development perspective (e.g., a single CSS class applied to a single CTA can be styled differently for different templates which load different stylesheets), in practice it seems that it would be more useful to see a button’s styles outside of a page context, particularly for non-developer users who may not know or remember that it requires multiple steps to style a button. For HubSpot themes and custom page templates which already include button styles, this might involve removing/refactoring/overriding those, but the end result would be a more portable style framework for HubSpot themes and CTAs overall.