`Development`: Fix issue with appearance of elements without attributes/methods having thicker bottom border

[minrows]

Checklist

• [x] I added multiple screenshots/screencasts of my UI changes

Motivation and Context

Classifier elements (class, abstract, interface ...) without attributes and methods used to have thicker bottom border. (Illustrated in before subsection of the section screenshot). This PR fixes the appearance of such elements by removing the thicker bottom border.

Steps for Testing

1. Clone the repo and checkout to enhancement/classifier-appearance branch
2. Run the application by executing yarn install followed by yarn start command
3. Insert element class or abstract or interface into the canvas
4. Remove all the attributes/methods of the inserted element
5. Observe that the thick border is not present anymore (as illustrated in the screenshot).

Screenshots

Before

After