Ability to specify a style library and custom class property
It would be helpful to be able to include a style library with a form or view. This would be simpler than modifying and maintaining a theme's CSS files. This feature would be greatly aided by the addition of a custom class property to objects. So that all controls in the designer would have a new property "Custom Class" which would be injected into the class attribute as specified and would allow the targeted application of CSS to elements. Even just the Custom Class property would go a long way.

Thank you for your feedback. Watch for the coming feature to add custom CSS into Style Profiles, releasing later this year for both K2 Five and K2 Cloud. You will be able to link external CSS files into your Style Profile to use in SmartForms, which should unlock this capability. Try it out when it releases and let us know your feedback. We aren't adding a specific Custom CSS Class field to each control, but you will be able to specify a custom CSS file in Style Profiles to affect styling.