Take a look at this drag and drop interaction for preparing a cup of tea and add states to the draggables and drop targets to make it look more realistic.

What is that example intending to do? When should the user use such a theme?

In this example, you will see the use of inbuilt states for draggables and drop targets to alter the appearance of objects. In your drag and drop interactions, you can easily customize the states for Drag sources and Drop targets, based on learner interaction and provide feedback, by altering the state of the drop targets to reflect whether an answer is correct or not.