Preview button style according to the context

Problem/Motivation

In Claro admin theme, the preview button looks like:

Button classes should be adjusted according to the context.

Steps to reproduce

Just enable the module in a site using Claro as the admin theme.

Proposed resolution

In Paragraphs, button classes are set according to the "item mode" that is determined after a complex logic. Copy classes from existing button could be a way of avoid calculation of the appropriate button classes.

Remaining tasks

Review.

User interface changes

None.

API changes

N/A

Data model changes

N/A