We now offer a custom CSS editor as part of the Pro plan.
Once you have signed up for the Pro plan, when you go to the Appearance page (/admin/theme or go to setup home and click on the Appearance card at the bottom of the page) then you will have access to the CSS editor at the bottom of the page
CSS editor in action
The editor contains auto complete and has error checking. You will see that the autocomplete is dynamic so that you can quickly search for fields and pages to style.
Clicking Save Custom CSS will instantly update the CSS on the page.
Current Class List
This is the list of top level classes in the application. We also add style/table/page and field namespacing so that you are able to target specific elements if you need to.