All Submissions:

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other openPull Requests for the same update/change?

New Feature Submissions:

1. Does your submission pass tests?
2. Have you lint your code locally prior to submission?

Changes to Core Features:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your core changes, as applicable?
• Have you successfully ran tests with your changes

Usage

Add:

ui.laf = com.formdev.flatlaf.FlatDarkLaf

totheme.txt, from custom theme

Next, install custom theme. (#10202 ).

Example

Sample Dark theme in attachments.
darkduino.zip
Need add jar from (#9815 ) or download:https://bintray.com/jformdesigner/flatlaf/flatlaf/0.34#files/com/formdev/flatlaf/0.34