You have to manually type the name of the CSS-class in the widget. This can lead to a lot of typing let alone typos so that the desired class is not selected.
Nice to have:
A dropdownlist of available CSS-classes replaces this. This way, you can very fast apply the custom style you would like to apply.
Besides that, a kind of suggestion of CSS to be applied could be useful eg. Background Green as a title and then the styling would be applied automatically.
You can achieve this by creating your own design properties, edit the settings.json in the theme folder:
One step further would be to have a” Stylesheet Editor” in Mendix Studio Pro itself.
E.g. In Mendix Studio Pro Stylesheet Editor you get the “Themes” folder → click on any file available within the themes folder → Edit the file in Mendix Studio Pro Stylesheet Editor → Compile Styling