Follow-up from changes introduced with new graph format

Problem/Motivation

In ✨ Add flowchart graph format Fixed , we introduced a new views style plugin, among other things. Some of the options there are not supported by the erDiagram plugin (ref. comment #12 ✨ Add flowchart graph format Fixed ).

There's also an opportunity to consolidate some code (eg. theme options), and potentially other refactoring. This'd benefit from adding tests as well.

Steps to reproduce

TBD

Proposed resolution

TBD

Remaining tasks

TBD

User interface changes

TBD

API changes

N/A

Data model changes

N/A