May Hubspot provide an option to use pseudo classes in the custom CSS such as :hover and :before? Hover effects can be an essential part of consistent UX and branding, and the same goes for special characters that appear on buttons such as icons based on a different font and other visual effects based on :before and :after.
Related post: https://community.hubspot.com/t5/CMS-Development/How-do-you-add-a-Custom-CSS-hover-class-to-a-call-t...
Suggested by Joe W