My suggestion is to improve the components area, as the visual aspect is already established and cannot be changed. For example, there’s a component called “radio” or even “checkbox.” However, if the designer needs to place a label around this input, they’ll need to do so outside the visual area, creating a selector group. For a framework the size of Core Framework, it would be much better if the designer could simply paste HTML code and style it visually, creating a “codepen.io” just for styling. An improvement of this magnitude could even be paid for if necessary.
I believe this would be a significant difference compared to other frameworks at the same level, as they all have a technical trick, but none have this native solution.
Detail: only CSS would be made available to the Builder, that is, it would not change the core framework’s business rules much.