Button styles need reset to avoid inheriting from theme

I've added a CSS reset for all buttons inside admin toolbar. With reset:

Setting this back to Needs review, since this could still be a temporary solution before this issue could really be properly addressed in ✨ Tabbing order does not satisfy 508 accessibility requirements Active .

Requalifying as Feature request since this is not actually preventing the proper use of the module.
It should maybe not be considered as a problem currently, but rather an improvement.

Additionally, the changes from merge request MR !53 don't seem to work anymore:

I didn't manage getting the chevron icons displayed locally by adding the piece of CSS to my code locally.

Thus moving issue to Needs work.

Any feedback, comments or reviews would be greatly appreciated.
Thanks in advance!