Fix bulk action buttons hover style

[djhi]

Problem

Buttons (especially BulkDeleteButton) look weird on hover in the BulkActionToolbar.

Solution

• Remove the default styles applied in the components code.
• Adjust the themes so that they look nice

How To Test

• make run-demo
• http://localhost:8000/#/orders
• Check the select all checkbox
• Move hover each button of the BulkActionToolbar
• Check all themes in both light and dark mode

Additional Checks

• The PR targets master for a bugfix or a documentation fix, or next for a feature