Upload and reference a different style sheet
To piggy back onto the custom class property (https://ideas.k2.com/ideas/APIT-I-187) . It would also be nice to be able to apply a custom style sheet to the application. During the application creation, the user could attach a custom style sheet (or a duplicate of the current one could be added.) All forms and views would use this style sheet and the developer could make changes to the style sheet, add new class rules, upload a replacement in the event they worked on one offline.
When you went to the style panel for a control, it could show you the default settings created by the specific rule on the style sheet. The style rule itself would be visible and an clickable object. The developer could click on the rule and they could edit the rule to make a global change or they could continue with the style panel and create an inline rule. If a global rule is changed and the rule is used by multiple selectors, the tool would need show the other selectors the change would impact. The user could then choose to impact all the selectors or break the one selector off into its own separate rule grouping.